Kenichi the Mightiest Disciple
Yomi no Kage
Trained by Saiga
After Kenichi and Ryuto's encounter with Miu, both boys fight for ownership of the yin-yang badge. But despite the arousal of his fighting spirit, Kenichi lost the battle because of Ryuto's natural talent. When Kenichi started begging for a retry over the next few days, Ryuto told him to shut up because he'd lost the fight and thus had no right. Kenichi took that reprimand literally and becomes obsessed with becoming the best martial artist in the world.
Unknown to either boy, their fight had been witnessed by Furinji Saiga. Saiga had seen Ryuto's natural talent, but his interest had been captured by what little of Kenichi's fighting spirit he'd seen. He decided to return in a few years to see whether he developed that spirit or left it unused.
Ryuto would quickly set himself to learning martial arts immediately afterwards so that he could relive that feeling of total victory over his opponent, he sought power for power's sake. Kenichi initially sought power to avenge his loss to Ryuto and to 'earn the right' to fight and take back the badge. But after a while, he had begun to enjoy fighting and the adrenaline rush of battle.
Five years later, Saiga found Kenichi (13) caught in a street fight against six older guys, all martial artists of entry level skill. Seeing them on the verge of unknowingly delivering a critical blow, he quickly intervenes, saving Kenichi's life, and scaring the punks off with a sliver of his killing aura. However, he was unprepared for Kenichi to suddenly latch onto him and demand training. Amused but not adverse to it, he decides to meet Kenichi's family and inspect his personality first. Shirahama Saori invites him to dinner as thanks when it's revealed he'd saved Kenichi's life. After the dinner, meeting the family, and speaking to Kenichi about his goals in martial arts, Saiga finally decides to take Kenichi as his own first ever disciple. With permission from his parents and the promise of continuing his normal education, Saiga takes Kenichi on a training journey all over the world as he teaches him the basics of his style.
Three years later…
Kenichi has slowly begun to grow out of his disciple clumsiness and is on his way to becoming a master. Within Yami, he has become known as the Kage, the shadow leader of Yomi. Unlike the rest of Yami's disciples, Kenichi never interacts with his companions in Yomi because he's too focused on becoming the strongest ever. But for all his training, he is still a largely unassuming and compassionate person who dislikes fighting without a reason and protecting the defenseless.
When he returns to his hometown for a small break, he finds it overrun by a martial arts gang that is headed by a mysterious disciple-class fighter called Odin. Intrigued, Kenichi decides to observe the fights. Much to his surprise and amusement, Saiga's daughter Miu was one of the key figures who had gotten caught up in the fights, thanks to Niijima's 'Taikyokuken Alliance' (Grand Ultimate Fist). Kenichi was eventually noticed by people on both sides, a mysterious cloaked figure hidden in the shadows who watched every fight take place.
When he finally attracted Odin's attention enough to warrant a fight during the final showdown between the two gangs, both Odin and Kenichi are surprised to learn they know each other. But when Kenichi politely asks for the badge, Odin refuses. Kenichi was able to triumph in the ensuing fight despite Ryuto's dou/sei ki. With his win, he finally reclaims his lost badge, much to the confusion of Ragnarok and the Taikyokuken. Only Miu is able to understand the significance and their unexpected bond through that badge. Hayato is able to recognize Saiga's style in Kenichi's moves and it was Ogata's proclamation that sealed his realization that Yami was beginning to move again.