Billion Girl

Billion Girl (ビリオンガール) is a shōjo manga series created by Miwa Sakai.

The first volume has been published by Hakusensha and ran in Hana to Yume magazine. Later it ran in Asuka, and all volumes (including the first one) have been published by Kadokawa Shoten.

Story
Kanoko Ooba is a 16 year old innocent girl currently attending high school. Her family owns a traditional Japanese sweets shop since the Meiji period. When her family's company becomes bankrupt, a mysterious stranger offers to pay their family's debt, in exchange, he wishes to marry one of the daughters of the Ooba family. When Kanoko's two elder sisters refused to be married, Kanoko volunteered herself in hopes of saving her family.

Characters
Kanoko is the youngest daughter of the old Japanese Confectionary shop "Ooba", which is on the verge of bankruptcy. She has 2 sisters who bully her around. She marries Houjo in exchange for her family debts to be paid.
 * Kanoko Ooba

He is the Houjo Family's 17th successor. He married Kanoko in exchange for the one billion dollar loan. He gets lonely rather easily thus he has a playboy image. Also, his job is as a porn novelist whose works Kanoko was set up by her friends to read out loud during class.
 * Taiga Houjo

Amamiya is Kanoko's classmate. He is very handsome but speaks in a somewhat feminine way. He likes messing with Kazuma. It's mentioned that he has had a hard life when looking up Kanoko's family registery. Amamiya has a caring personally and doesn't like any of the other girls in the class.
 * Yasuhito Amamiya

He is the Houjo family's super efficient house keeper and is in charge of managing Houjo. He has a very helpful personality, doing everything he is told.
 * Obinata

Oshinari, Kanoko's classmate, is secretly in love with Kanoko. However, it's not really a secret. In his 1st year all the girls in his class were to give him chocolates for Valentine's day. The task of giving him the chocolates was given to Kanoko thus leading him to believe they were from her. She told him they weren't and he's been bitter to her since.
 * Kazuma Oshinari

Mibu is a smart first year high school student who wants to take over Ooba Confectionary shop when he gets older. Mibu works as a spy for Oshinari and Amamiya as the apprentice at the Ooba shop.
 * Tatsuya Mibu

Reo is Houjo's elder half-brother and half-cousin. Reo's mother is Houjo's mother's twin sister. As a result, he hates Houjo and his mother. Reo wants to steal Kanoko away for revenge, blaming Houjo for killing his sister, Tokiko, who actually drowned in a pond.
 * Reo Ijuuin

Volumes

 * 1) ISBN 4-04-924867-0 released on June 16, 2001
 * 2) ISBN 4-04-924868-9 released on June 16, 2001
 * 3) ISBN 4-04-924871-9 released on August 17, 2001
 * 4) ISBN 4-04-924894-8 released on January 17, 2002
 * 5) ISBN 4-04-924908-1 released on July 17, 2002
 * 6) ISBN 4-04-924920-0 released on November 16, 2002
 * 7) ISBN 4-04-924939-1 released on March 17, 2003
 * 8) ISBN 4-04-924939-1 released on September 17, 2003
 * 9) ISBN 4-04-924961-8 released on April 17, 2004
 * 10) released on October 16, 2004