K-On!

K-On! (けいおん!) is a Japanese four-panel comic strip manga written and illustrated by Kakifly. The manga was serialized in Houbunsha's seinen manga magazine Manga Time Kirara between the May 2007 and October 2010 issues. It was also serialized in Houbunsha's magazine Manga Time Kirara Carat. A 13-episode anime adaptation produced by Kyoto Animation aired in Japan between April and June 2009. An additional original video animation episode was released in January 2010. A 26-episode second season, titled K-On!! (with two exclamation marks), aired in Japan between April and September 2010. An anime film adaptation has been announced. The title of the series comes from the Japanese word for light music, keiongaku (軽音楽), but in the Japanese context is similar to pop music.

Plot
K-On!'s story revolves around four Japanese high school girls who join their school's light music club to try to save it from being abolished. However, they are the only members of the club, and at first Yui Hirasawa, the main character, has no experience playing musical instruments or reading sheet music. Eventually, she learns how to be an excellent guitar player. Since then, Yui, bassist Mio Akiyama, drummer Ritsu Tainaka and keyboardist Tsumugi Kotobuki spend their school days practicing, performing, or just hanging out together. The club is overseen by music teacher Sawako Yamanaka, who eventually becomes their homeroom teacher as well during their final year of high school. In their second year of high school, the club welcomes another guitarist, an underclassman named Azusa Nakano. After Azusa joins, they gain more structure and begin to practice more. The story concludes at the end of the third year for the senior members. They all agree to attend the same university after high school and leave the club to Azusa after graduation. Yui's sister, Ui, and their friend Jun both join the club for Azusa's senior year.

Characters
Toshimi Yotsumoto of ASCII Media Works pointed out that the characters of K-On! have surnames derived from members of the Japanese bands P-Model and The Pillows. The five main characters are members of a band, Ho-kago Tea Time (放課後ティータイム), which performs the theme songs in the anime.

Ho-kago Tea Time

 * Yui Hirasawa (平沢 唯)
 * Yui is the main character of K-On!. She is one of the members of the light music club and plays a Heritage Cherry Sunburst Gibson Les Paul Standard electric guitar that she nicknames "Gīta" (ギー太). She does not get good grades in school (though when properly coached, she can achieve astounding results) and is easily distracted by trivialities (mainly those deemed cute and adorable). Yui is clumsy and easily spaces out most of the time. Yui has shoulder-length, brown hair (a little longer than Ritsu's) which she accessorizes with two yellow hair clips, and brown eyes. She takes a huge liking for any kind of food (she practically never gains weight, which is greatly envied by Mugi, Mio, and Sawako ). She has her younger sister Ui, who is the very mature and down-to-earth opposite of Yui, to take care of her and keep herself in line. Yui works extremely hard to get better at playing guitar, which is shown in later chapters. During performances, Yui plays with amazing energy and joy, which usually results in great response from the audience.
 * Yui is the main character of K-On!. She is one of the members of the light music club and plays a Heritage Cherry Sunburst Gibson Les Paul Standard electric guitar that she nicknames "Gīta" (ギー太). She does not get good grades in school (though when properly coached, she can achieve astounding results) and is easily distracted by trivialities (mainly those deemed cute and adorable). Yui is clumsy and easily spaces out most of the time. Yui has shoulder-length, brown hair (a little longer than Ritsu's) which she accessorizes with two yellow hair clips, and brown eyes. She takes a huge liking for any kind of food (she practically never gains weight, which is greatly envied by Mugi, Mio, and Sawako ). She has her younger sister Ui, who is the very mature and down-to-earth opposite of Yui, to take care of her and keep herself in line. Yui works extremely hard to get better at playing guitar, which is shown in later chapters. During performances, Yui plays with amazing energy and joy, which usually results in great response from the audience.


 * Yui is the band's main vocalist and lead guitarist and has absolute pitch—she can tune her guitar perfectly without a tuner, which greatly impresses Azusa, who has played the guitar much longer than Yui. She has a very easy-going nature, but has incredible focus and retention when she has a clear goal in sight; unfortunately this is limited to only one subject at a time, and her other skills deteriorate quickly (for example, Yui is at one point pressed to make up failing test scores, and she quickly brings her math skills up to par while allowing her guitar skills to deteriorate.) Despite all of this, Yui is still devoted to her band and will always practice hard enough for the club. At school, she has become quite admired for her great voice. However, she is known to forget her lyrics in mid-performance as well as overdoing things, making her unable to perform sometimes. Mio was the lead vocalist at first, since Yui could not play the guitar and sing at the same time. Yui is also known to write childish lyrics as Ui has assisted her in creating them.


 * Ritsu Tainaka (田井中 律)
 * Ritsu (or Rit-chan, as nicknamed by Yui) is the self-proclaimed president of the light music club and plays a yellow Rick Marotta Signature Yamaha Hipgig drum kit with an add-on floor tom (in the opening credits only) combined with a cymbal set from Avedis Zildjian, though is shown playing a white Yamaha Absolute Series drumkit in the anime's closing credits. She has an ambiguous yet upbeat personality, much like Yui, but often has trouble remembering important club activities and announcements and gets constantly rebuked by Mio and Nodoka for forgetting to send in important forms concerning the club. Ritsu is cheerful, often likes making jokes and is sarcastic most of the time. She is skilled at brainstorming ideas that earn money for the club. Ritsu has shoulder-length, brown hair, with her bangs pulled back with a yellow hairband, and gold-colored eyes. She wears her school jacket open. She says she chose to play the drums because they are "cool", but she then admits that she has trouble playing instruments which involve intricate finger movements, such as the bass, guitar and keyboard.
 * Ritsu (or Rit-chan, as nicknamed by Yui) is the self-proclaimed president of the light music club and plays a yellow Rick Marotta Signature Yamaha Hipgig drum kit with an add-on floor tom (in the opening credits only) combined with a cymbal set from Avedis Zildjian, though is shown playing a white Yamaha Absolute Series drumkit in the anime's closing credits. She has an ambiguous yet upbeat personality, much like Yui, but often has trouble remembering important club activities and announcements and gets constantly rebuked by Mio and Nodoka for forgetting to send in important forms concerning the club. Ritsu is cheerful, often likes making jokes and is sarcastic most of the time. She is skilled at brainstorming ideas that earn money for the club. Ritsu has shoulder-length, brown hair, with her bangs pulled back with a yellow hairband, and gold-colored eyes. She wears her school jacket open. She says she chose to play the drums because they are "cool", but she then admits that she has trouble playing instruments which involve intricate finger movements, such as the bass, guitar and keyboard.


 * She is a childhood friend of Mio and will often have the opportunity to tease her whenever she is cowering from something. She is also known to become easily jealous of Mio's other high school friends, even going as far as spying on her when on outings with them. Ritsu is always on the go and will stop at nothing for the success of the light music club. Despite her rough mannerisms and speech, she gets cast as Juliet by the majority of her classmates in their class play rendition of Romeo and Juliet and, in the end, manages to act like a proper girl. In the anime, she states her favorite drummer is Keith Moon of The Who. She is skilled at cooking. She has a younger brother named Satoshi (聡).


 * Mio Akiyama (秋山 澪)
 * Mio is a shy girl who is in the light music club. She plays a left-handed, 3-Color Sunburst Fender Jazz Bass with a tortoiseshell pickguard, though is shown playing a Fender Precision Bass in the first manga volume. She uses D'Addario EXL160M medium bass strings. While she originally intended to join the literary club, she was forced into the light music club by her childhood friend and the club's president/drummer, Ritsu. She gets excellent grades in school and is many times mature and strict especially where Ritsu is involved; her weakness is the macabre and horrific, and she is often incapacitated with fear when stories involving ghosts, blood, injuries, haunted houses, barnacles or other disturbing topics come up. She also has a fear of being in the spotlight and gets embarrassed easily, and is often subject to teasing from Ritsu and Sawako, their club adviser and eventual third-year homeroom teacher. Mio has long, straight black hair and gray eyes (that are angled slightly more than the other characters). She cites that she chose bass since it is not the center of attention in the band, unlike the guitarist. Mio is more technical when it comes to music, and Yui often comes to her when she is in need of more guitar tutorials.
 * Mio is a shy girl who is in the light music club. She plays a left-handed, 3-Color Sunburst Fender Jazz Bass with a tortoiseshell pickguard, though is shown playing a Fender Precision Bass in the first manga volume. She uses D'Addario EXL160M medium bass strings. While she originally intended to join the literary club, she was forced into the light music club by her childhood friend and the club's president/drummer, Ritsu. She gets excellent grades in school and is many times mature and strict especially where Ritsu is involved; her weakness is the macabre and horrific, and she is often incapacitated with fear when stories involving ghosts, blood, injuries, haunted houses, barnacles or other disturbing topics come up. She also has a fear of being in the spotlight and gets embarrassed easily, and is often subject to teasing from Ritsu and Sawako, their club adviser and eventual third-year homeroom teacher. Mio has long, straight black hair and gray eyes (that are angled slightly more than the other characters). She cites that she chose bass since it is not the center of attention in the band, unlike the guitarist. Mio is more technical when it comes to music, and Yui often comes to her when she is in need of more guitar tutorials.


 * Along with Yui, Mio is one of the band's main vocalists, though given her dislike of being center stage, she tries to avoid taking the lead vocal if possible, generally singing if Yui is unable to. She writes most of the songs, although they usually feature some odd and overly girlish lyrics like "Light and Fluffy Time". As she is left-handed, she becomes entranced whenever she sees left-handed instruments, because of their rarity. After their first live performance, the attractive Mio gained a huge fan following (in no small part due to an unfortunate accident that occurred at the end of the show), led by an infatuated former student council president. Also resulting from her sudden popularity, most of her classmates voted that she portray Romeo in their class play.


 * Tsumugi Kotobuki (琴吹 紬)
 * Tsumugi, often referred to as 'Mugi' by her friends, is a wealthy girl with a gentle and sweet personality who plays a Korg Triton Extreme 76-key keyboard, though she is also seen playing a Korg RK-100 keytar in the closing credits of the first season. She originally intended to join the choir club, but joins the light music club instead after receiving an invitation and encouragement from both Mio and Ritsu. Tsumugi is considered a piano prodigy since she has been playing the piano since she was four and has experience in winning various piano contests. Mugi has long, wavy blonde hair and sky-blue eyes. She is the daughter of a company president,  and her family has several villas in various places around Japan (and even one in Finland). Since her father also owns a maid café, she often brings confectionery and an assortment of sweets and pastries to the club room, and she diligently makes tea with a tea set which is kept in their club room. Despite her wealth, she is fascinated by and finds joy in "normal" activities, such as ordering fast food, sharing french fries with her club mates, holding down part-time jobs and haggling over prices.  Tsumugi displays a rebellious streak occasionally, diverting from her normally well-behaved and mature demeanor to the surprise of the others.
 * Tsumugi, often referred to as 'Mugi' by her friends, is a wealthy girl with a gentle and sweet personality who plays a Korg Triton Extreme 76-key keyboard, though she is also seen playing a Korg RK-100 keytar in the closing credits of the first season. She originally intended to join the choir club, but joins the light music club instead after receiving an invitation and encouragement from both Mio and Ritsu. Tsumugi is considered a piano prodigy since she has been playing the piano since she was four and has experience in winning various piano contests. Mugi has long, wavy blonde hair and sky-blue eyes. She is the daughter of a company president,  and her family has several villas in various places around Japan (and even one in Finland). Since her father also owns a maid café, she often brings confectionery and an assortment of sweets and pastries to the club room, and she diligently makes tea with a tea set which is kept in their club room. Despite her wealth, she is fascinated by and finds joy in "normal" activities, such as ordering fast food, sharing french fries with her club mates, holding down part-time jobs and haggling over prices.  Tsumugi displays a rebellious streak occasionally, diverting from her normally well-behaved and mature demeanor to the surprise of the others.


 * Although she is a sweet and gentle girl, she is often weirdly entranced by the sight of two girls interacting closely together, sometimes imagining something more risqué in her head (both Mio and Ritsu find this awkward at times). The series sometimes indicates that Mugi has a crush on their teacher, Sawako Yamanaka. While a lot of things do not bother her, she is fairly conscious about her weight (just like Mio), and she gets a bit anxious when her family's staff start spoiling her friends during villa visits. She later begins learning how to play the guitar from Azusa.


 * Azusa Nakano (中野 梓)
 * Azusa is a student in the same year and class as Yui's sister Ui, who joins the light music club and becomes the rhythm guitarist, playing a Fender Mustang electric guitar. She is a self-proclaimed novice guitarist who has been playing the guitar since she was in the fourth grade, and her parents are working in a jazz band. She often finds herself bewildered by the tea parties and cosplaying aspects of the club, when she would rather just practice, and is curious about how the club is able to play so well despite their problems and lack of practice. However, she has a certain weakness for cakes and can be calmed down rather easily, sometimes by just being petted. She is constantly a victim of Yui's skinship and is nicknamed Azu-nyan after trying on a pair of cat ears and meowing ("nyan" being the equivalent of "meow" in the Japanese vocabulary). Despite this, Azusa is not too good with cats. Azusa has long black hair, which she wears in pigtails, and red eyes.
 * Azusa is a student in the same year and class as Yui's sister Ui, who joins the light music club and becomes the rhythm guitarist, playing a Fender Mustang electric guitar. She is a self-proclaimed novice guitarist who has been playing the guitar since she was in the fourth grade, and her parents are working in a jazz band. She often finds herself bewildered by the tea parties and cosplaying aspects of the club, when she would rather just practice, and is curious about how the club is able to play so well despite their problems and lack of practice. However, she has a certain weakness for cakes and can be calmed down rather easily, sometimes by just being petted. She is constantly a victim of Yui's skinship and is nicknamed Azu-nyan after trying on a pair of cat ears and meowing ("nyan" being the equivalent of "meow" in the Japanese vocabulary). Despite this, Azusa is not too good with cats. Azusa has long black hair, which she wears in pigtails, and red eyes.


 * In the band, she looks up to Mio the most due to her maturity and the fact that she is an experienced bassist, even trying to give Mio chocolate on Valentine's Day. However, she sometimes unintentionally makes remarks concerning Mio's weaknesses, such as her weight. She also finds Mugi very beautiful, and envies her hair and large eyes, and later starts teaching her how to play guitar when the two are alone in the club room. Since joining, Yui comes to her for advice on playing guitar, as well as maintenance. She gets a tan extremely easily, once during their time at the beach and another during a music festival (even after applying sunscreen). As a result, she frequently gets sunburned as well. She gets lonely very easily, and often worries that everyone in the club will leave her, as they are one year older and eventually will graduate. Due to this, the rest of the girls buy her a turtle to look after, naming it Ton. Outside of the band, she often hangs out with Ui and Jun whenever the other girls are busy. When the others graduate, she becomes the new light music club president.

Secondary characters

 * Sawako Yamanaka (山中 さわ子)
 * Sawako is the adviser for the wind instrument club at the girls' school. An alumna of the school and a member of the light music club in her student days, she does not want people to find out that she was formerly a member of not only a heavy metal band, but a death metal band called Death Devil (of which she was both lead guitar and vocalist and went by the stage name of "Katherine" ), thus she covers up by being mild and gentle to her coworkers and especially to students. She is forced to be the adviser of the light music club, as Ritsu blackmails her after the girls learn of her past. However, she is able to juggle being the adviser for the wind instrument club as well, even as the story progresses. Though she has a mature and gentle demeanor in the school, Sawako (affectionately addressed as "Sawa-chan" by both Ritsu and Yui) displays a totally different, completely authentic character when she is alone with the light music club. In reality, she is rather wild, lazy, and is quite an irresponsible teacher who enjoys dressing up the light music club in (sometimes embarrassing) cosplay costumes (like French maid uniforms), much to the dismay of Mio. She gets a thrill out of the rare moments where she is praised for her work.
 * Sawako is the adviser for the wind instrument club at the girls' school. An alumna of the school and a member of the light music club in her student days, she does not want people to find out that she was formerly a member of not only a heavy metal band, but a death metal band called Death Devil (of which she was both lead guitar and vocalist and went by the stage name of "Katherine" ), thus she covers up by being mild and gentle to her coworkers and especially to students. She is forced to be the adviser of the light music club, as Ritsu blackmails her after the girls learn of her past. However, she is able to juggle being the adviser for the wind instrument club as well, even as the story progresses. Though she has a mature and gentle demeanor in the school, Sawako (affectionately addressed as "Sawa-chan" by both Ritsu and Yui) displays a totally different, completely authentic character when she is alone with the light music club. In reality, she is rather wild, lazy, and is quite an irresponsible teacher who enjoys dressing up the light music club in (sometimes embarrassing) cosplay costumes (like French maid uniforms), much to the dismay of Mio. She gets a thrill out of the rare moments where she is praised for her work.


 * She names the club band "Ho-kago Tea Time" after the members take too long deciding on a name themselves. In the anime, she once pitches in for Yui with her white Epiphone "1958" Korina Flying V electric guitar. She becomes the girls' homeroom teacher in their third year, and puts Nodoka and all the band members (except Azusa, since she is a grade lower) in the same class, so she does not have to remember as many names. An episode in the second anime season reveals that she owned one of the first Gibson SG models (from around 1960 with a custom stoptail bridge) which is later sold. Due to her relation to the club members, the other students in her class start to call her Sawa-chan as well, ruining her image as a mild-mannered teacher. Her image is further ruined after Death Devil is temporarily reunited at a wedding reception for a high school alumnus. Regardless, her popularity with the students remains unchanged. In spite of her laziness, she still proves herself to be an able mentor, as shown by her willingness to coach Yui as the lead singer and attending their performances. Her music abilities apparently have not dulled over the years, as she is able to substitute for Yui at the school festival at almost no notice without the assistance of a music score, even without any prior practicing of the band's song. Sawako is also very perceptive: she immediately sees through Ui's disguise when she impersonates her sister and on several occasions boasts to the club that there is nothing she cannot see.


 * Ui Hirasawa (平沢 憂)
 * Ui is Yui's younger sister, who begins the story as a third-year junior high school student, but later enters Yui's high school the following year in the same class as Azusa. Unlike her older sister, Ui is mature, responsible, and handles household chores well, though she still shares a strong relationship with Yui and has a great deal of love and respect for her older sister. Despite being a year younger than Yui, she is nearly identical to her with her hair down and is even once able to fool the club. She plays the organ, and is also a fast learner, able to learn playing the guitar after a few days' practice. She takes particularly good care of Yui and strives to look after her even at the risk of her own health.  Ui is actually considered as the ultimate groupie for her sister's band and supports them with all her heart and occasionally provides a narrative to the story. She eventually joins the light music club along with Jun at the end of the series.
 * Ui is Yui's younger sister, who begins the story as a third-year junior high school student, but later enters Yui's high school the following year in the same class as Azusa. Unlike her older sister, Ui is mature, responsible, and handles household chores well, though she still shares a strong relationship with Yui and has a great deal of love and respect for her older sister. Despite being a year younger than Yui, she is nearly identical to her with her hair down and is even once able to fool the club. She plays the organ, and is also a fast learner, able to learn playing the guitar after a few days' practice. She takes particularly good care of Yui and strives to look after her even at the risk of her own health.  Ui is actually considered as the ultimate groupie for her sister's band and supports them with all her heart and occasionally provides a narrative to the story. She eventually joins the light music club along with Jun at the end of the series.


 * Nodoka Manabe (真鍋 和)
 * Nodoka is Yui's childhood friend and confidant who is a member of the school's student council. As a normal, well-mannered and intelligent girl, she is generally taken aback by the light music club's odd behavior, and easily gets annoyed with Ritsu whenever she forgets to fill in the club's application forms. She shares the same class as Mio in their second year, who appreciates her companionship tremendously, she being the only person Mio knows in her class. In her third year, she becomes the student council president and is also in the same class as the other third year club members. She gradually becomes the president of Mio's fan club through unknown circumstances (possibly out of her control), even when she originally turned down the position. Nodoka chooses to go to a national university as opposed to the same college as Yui and the others.
 * Nodoka is Yui's childhood friend and confidant who is a member of the school's student council. As a normal, well-mannered and intelligent girl, she is generally taken aback by the light music club's odd behavior, and easily gets annoyed with Ritsu whenever she forgets to fill in the club's application forms. She shares the same class as Mio in their second year, who appreciates her companionship tremendously, she being the only person Mio knows in her class. In her third year, she becomes the student council president and is also in the same class as the other third year club members. She gradually becomes the president of Mio's fan club through unknown circumstances (possibly out of her control), even when she originally turned down the position. Nodoka chooses to go to a national university as opposed to the same college as Yui and the others.


 * Jun Suzuki (鈴木 純)
 * Jun is Azusa's and Ui's classmate who often hangs out with the latter. Ui tries to get her to join the light music club but ultimately fails due to a strange visit to the club room. She instead plays a Yamaha Sbv500 bass in the jazz club and is one of Mio's admirers. However, she starts to regret not joining the light music club when she hears about all the activities they do and eventually joins the light music club at the end of the series. She has a pet cat.
 * Jun is Azusa's and Ui's classmate who often hangs out with the latter. Ui tries to get her to join the light music club but ultimately fails due to a strange visit to the club room. She instead plays a Yamaha Sbv500 bass in the jazz club and is one of Mio's admirers. However, she starts to regret not joining the light music club when she hears about all the activities they do and eventually joins the light music club at the end of the series. She has a pet cat.


 * Megumi Sokabe (曽我部 恵)
 * Megumi was the president of the student council before Nodoka succeeded her in her third year, and she is also the president of Mio's fan club, who is later succeeded by Nodoka. She stalks Mio during her last few days in high school because she wanted to see Mio one more time. The band offers her a song as a graduation gift. She later becomes friends with Ritsu, mentioning she is at the same university the others intend to go to.
 * Megumi was the president of the student council before Nodoka succeeded her in her third year, and she is also the president of Mio's fan club, who is later succeeded by Nodoka. She stalks Mio during her last few days in high school because she wanted to see Mio one more time. The band offers her a song as a graduation gift. She later becomes friends with Ritsu, mentioning she is at the same university the others intend to go to.

Manga
K-On! began as a four-panel comic-strip manga written and illustrated by Kakifly. The manga was serialized in Houbunsha's Manga Time Kirara manga magazine between the May 2007 and October 2010 issues, ending on September 9, 2010. The manga has also appeared as a guest bimonthly serialization in Manga Time Kirara's sister magazine Manga Time Kirara Carat starting with the October 2008 issue. The first tankōbon volume was released on April 26, 2008; the third volume was released on January 2, 2010. A fourth and final volume will be sold on September 27, 2010. The manga was licensed by Yen Press for an English release in North America. In Indonesia, the series is licensed by Elex Media Komputindo. There is an anthology entitled Minna de Untan!, which features several guest strips from various artists. An official anthology, K-On! Anthology Comic (けいおん!アンソロジーコミック), was released on November 27, 2009 by Houbunsha, with a second volume being released on April 27, 2010. An illustration book with official art and fan art from well known dōjin artists was released on January 27, 2010.

Anime
A 13-episode anime adaptation directed by Naoko Yamada, written by Reiko Yoshida, and produced by Kyoto Animation aired between April 3 and June 26, 2009 on TBS in Japan. The episodes began airing on subsequent networks at later dates which include BS-i, MBS, and Chubu-Nippon Broadcasting. The TBS airings are in 4:3 ratio, and the series began airing in widescreen on BS-TBS on April 25, 2009. Seven BD/DVD compilation volumes were released by Pony Canyon between July 29, 2009 and January 20, 2010. An additional original video animation (OVA) episode was released with the final BD/DVD volumes on January 20, 2010. Animax has aired the anime in Hong Kong and Taiwan. Both an English-subtitled and English-dubbed version by Red Angel Media began airing on March 16, 2010 on Animax Asia. At their industry panel at Anime Expo 2010, anime distributor Bandai Entertainment announced that they have acquired K-On! for a DVD and Blu-ray Disc release, with Bang Zoom! Entertainment producing an English dub for the show. The series will be released over four volumes in standard and limited editions for each format, starting in spring 2011. Manga Entertainment will release the series in the UK.

It was displayed on screen at the Let's Go live concert in Yokohama, Japan on December 30, 2009 that a second season would be produced. The second season, titled K-On!! (with two exclamation marks), aired with 26 episodes on TBS in Japan between April 7, 2010 and September 28, 2010. An additional OVA episode will be released with the final BD/DVD volumes on March 16, 2011. This season has also aired on Animax Asia starting October 20, 2010.

Film
After the final TV anime episode of K-On!! aired, an anime film was announced to be in production by Kyoto Animation.

Music
The first season anime's opening theme is "Cagayake! Girls" by Aki Toyosaki with Yōko Hikasa, Satomi Satō and Minako Kotobuki. The ending theme is "Don't Say 'Lazy'" by Hikasa with Toyosaki, Satō and Kotobuki. The opening and ending theme singles were released on April 22, 2009. A single containing the insert song "Fuwa Fuwa Time" (ふわふわ時間) used in episode six was released on May 20, 2009. A series of character song singles have been released containing songs sung by the voice actresses of the five main characters. The singles for Yui (by Toyosaki) and Mio (by Hikasa) were released on June 17, 2009. The singles for Ritsu (by Satō) and Tsumugi (by Kotobuki) were delayed, but later released together with the single for Azusa (by Ayana Taketatsu) on August 26, 2009. The singles for Ui Hirasawa (by Madoka Yonezawa) and Nodoka Manabe (by Chika Fujitō) were released on October 21, 2009. The anime's original soundtrack, largely composed by Hajime Hyakkoku, was released on June 3, 2009. The four songs highlighted in episode eight of the anime were released on the mini album Ho-kago Tea Time (放課後ティータイム) on July 22, 2009. The single "Maddy Candy" by Sawako's band Death Devil was released on August 12, 2009.

The second season anime's first opening theme is "Go! Go! Maniac" and the first ending theme is "Listen!!"; both songs are sung by Toyosaki, Hikasa, Satō, Kotobuki, and Taketatsu. The singles containing the songs were released on April 28, 2010. From episode 14 onwards, the respective opening and ending themes are "Utauyo!! Miracle" and "No, Thank You!", both by Toyosaki, Hikasa, Satō, Kotobuki, and Taketatsu. The singles containing these songs were released on August 4, 2010. The single "Pure Pure Heart" also sung by Toyosaki, Hikasa, Satō, Kotobuki, and Taketatsu was released on June 2, 2010. Another single, "Love", by Sawako's band Death Devil was released by on June 23, 2010. A single sung by Toyosaki, "Gohan wa Okazu/U&I", was released on September 8, 2010. The composer Bice who wrote the song "Gohan wa Okazu" died on July 26, 2010 of a heart attack. A second set of character song singles were released, starting with the singles for Yui and Mio on September 21, 2010. The show's second album, Ho-kago Tea Time II, was released on both normal double CD and limited edition that came with a cassette tape on October 27, 2010. The singles and albums were released by Pony Canyon.

Video game
A rhythm video game titled K-On! Hōkago Live!! (けいおん! 放課後ライブ!!), developed by Sega for the PlayStation Portable, was released on September 30, 2010. The gameplay involves the player matching button presses in time with music featured in the anime. The game supports local multiplayer for up to five PSPs. The game features 19 songs from the first anime season and first set of character song CDs. The player can customize the clothing, hair style and accessories of the characters, plus customization of the light music room and Yui's bedroom. There is also a custom track maker.

Reception
The first manga volume of K-On! was the 30th highest-selling manga volume in Japan for the week of April 27 and May 3, 2009, having sold over 26,500 volumes that week. The following week, the first and second manga volumes were the 19th and 20th highest-selling manga volumes in Japan, having sold 23,200 and 22,500 volumes each the week of May 4 and May 10, 2009. As of May 2009, the first two manga volumes each sold about 136,000 copies each. The third volume sold over 120,000 copies the week of December 14–20, 2009, and became the 46th top-selling manga for the first half of 2010 in Japan (ending May 23), selling over 328,000 copies.

The single for the first anime's opening theme, "Cagayake! Girls", debuted at fourth in the ranking on the Oricon weekly singles chart, selling approximately 62,000 copies. The ending theme "Don't Say 'Lazy'" debuted at second in the ranking, selling 67,000 copies. It was also awarded Best Theme Song at the 14th Animation Kobe Awards. Additionally, "Cagayake! Girls" and "Don't Say 'Lazy'" were certified Gold and Platinum by the Recording Industry Association of Japan (RIAJ) for 100,000 and 250,000 full-track ringtone digital music downloads (Chaku Uta Full), respectively. The mini album Ho-kago Tea Time debuted at No. 1 on the Oricon weekly CD albums charts selling 67,000 copies, making it the first image song album credited to fictional anime characters that reached the highest position. The second anime's opening theme "Go! Go! Maniac" and ending theme "Listen!!" debuted at No. 1 and No. 2 in their first week of release on the Oricon singles chart, selling over 83,000 and 76,000 copies, respectively. "Go! Go! Maniac" became the first anime image song to ever top the singles chart and the band also became the first female vocalists to occupy the top two spots on the singles chart in 26 years since Seiko Matsuda in 1983. The season's second ending and opening themes, "No, Thank You!" and "Utauyo! Miracle" respectively, sold 87,000 and 85,000 in their first week and ranked at No. 2 and No. 3 in the Oricon charts respectively, only being beaten by SMAP's single, "This is Love". "No, Thank You!" and "Utauyo! Miracle" were certified Gold by the RIAJ in August 2010 for 100,000 copies shipped. The single "Gohan wa Okazu"/"U&I" debuted at No. 3 on the Oricon singles chart, selling 53,000 in its first week. The album Ho-kago Tea Time II debuted at No. 1 on the Oricon weekly CD albums charts selling 127,000 copies.

The first Japanese DVD volume of the anime series sold around 8,000 copies to debut seventh in the ranking on the Oricon charts for the week of July 29, 2009. The Blu-ray Disc release of the first volume sold about 33,000 copies in the same week, to top the Oricon BD charts. In August 2009, the first volume of K-On! was the top-selling television anime Blu-ray Disc in Japan, having surpassed the previous record holder Macross Frontier, which sold approximately 22,000 copies of its first volume. It was the second best-selling Blu-ray Disc in Japan, trailing only Evangelion: 1.0 You Are (Not) Alone, with around 49,000 copies. However, in October 2009, the first volume of Bakemonogatari surpassed K-On!'s previous record, having sold 37,000 copies at that time. Later, with the release of K-On!! volume 3, total BD sales for the series have outsold Bakemonogatari. K-On! received a Best TV Animation Award at the 2010 Tokyo International Anime Fair. K-On!! won the Best Television award at the 2010 Animation Kobe Awards.

At the beginning of September 2010, the Kyoto prefectural government began using K-On!! to promote the census and encourage people to be counted.