He is a Juraian scientist who specialized in swords and swordplay, and even designed the energy sword used by Ryoko. Like Kagato, Yakage studied under Washu as one of her personal assistants at the Galactic Academy, but possessed a greater sense of honor and loyalty than the future "Ruins Buster". Despite this, he was not without ambition or obsession, and Yakage became immersed into creating a sword of immense power, one that would be strong enough to even overcome the Lighthawk Wings.
To reach that goal, Yakage abandons Washu, stealing some of Ryoko's DNA and mixing it with his own. He began raising and training his Ryoko, named Minagi, to be a superior warrior, planning for her to be the wielder of this "ultimate sword". Though harsh - and on occasion, brutal - in his teachings, Yakage genuinely cares for Minagi, only wanting his daughter to be prepared for whatever trials she might face in the future. The full extents of his research are still unknown, but he did discover many powerful blades, some so valuable they were sought by others themselves (and subsequently taken from his possession). The culmination of his work was a dual-bladed, artificial Lighthawk Sword.
Yakage managed to stay for thousands of years to further his studies by cloning himself each time he was near death, training Minagi in the ways of swordsmanship all the while. However, the cloning wasn't perfect, making each version of the scientist weaker than the last. Cell degeneration had set in, and with Yakage growing sickly - bad off enough to suffer spurts of coughing up blood at points - Minagi confronted Tenchi and the others on Earth. She attacks them knowing that they were the one who defeated Kagato, thinking research on Tenchi's sword would help her master achieve his greatest wish. However, Minagi was beaten by Ryoko, and was stricken with amnesia as a result.
New test subjects
His protegé missing, Yakage comes to earth along with his two guardians, Kuze and Hakkou, interested in seeing the power of the Lighthawk Sword. During this encounter, Kuze and Hakkou easily dispatched Tenchi, and Yakage, lecturing the boy about his lack of focus, took Ayeka prisoner in order to entice Tenchi into facing him with his full force. Though Yakage is mindful of taking the girl (as she is First Princess of Jurai), as a scientist he must use whatever means are necessary to carry out his research.
Ryoko failed in her attempt to defeat Yakage alone (to keep Tenchi from having to fight him), so Tenchi and the others quickly headed off to Yakage's ship to take him down. Through fighting with him, Minagi's memories gradually return, and after seeing the scar on his face - something Yakage kept as a memento of the first time Minagi bested him in combat - she remembers everything. Minagi allows herself to be cut down by Yakage's final strike, desiring to help achieve his dreams and make her father happy. Yakage had never told her that he only wanted to prove the sword's abilities in combat so he could give it as a gift to her.
Still unwilling to waver with Minagi's sacrifice, Yakage refused to quit until he and Tenchi have a final match, for the sake of both his research and his daughter. The scientist tries to goad the boy into battle by threatening Ayeka and Ryoko's lives, as a shield surrounding them will eventually kill them unless Yakage himself dies first. As they fight, Washu reveals that this Yakage is a copy, as he's been repeating himself millennium after millennium, overwriting his knowledge and appearance until his body could no longer withstand the constant degeneration.
Not wanting to kill Yakage - despite knowing the scientist's life was nearly at its end - Tenchi and his friends were put into serious jeopardy themselves. Ryoko breaks free of her bonds to save Tenchi from Yakage's deathblow, but it's not until the scientist levels his weapon at Ryoko that Tenchi shows his true power. The two then trade sword strokes, with Yakage cleaved in two by the inferiority of his artificial sword against the genuine article. Having done his best as a scientist and warrior, Yakage's only regret is that he won't be able to pass the sword along to Minagi, as he bids the group a final farewell.
- Like many characters in Tenchi Muyo!, Yakage takes his name from a locale around Japan's Okayama Prefecture, in this case a town located within the Oda District.
- Since VIZ's initial pressings of No Need for Tenchi! were "flipped" (i.e. reversed horizontally from the original right-to-left for a more natural read to Westerners) the mirror effect caused several errors to Okuda's artwork. One can be seen above, as Yakage's scar runs under his right eye instead of curving to the left. Currently, a second edition of the books is being released in the un-flipped format.