Leader of the Santoryu Team and the strongest among the trio, Kaku holds deep resentment towards Kensei Ma, stating that "anything related to the Ma family must be exterminated, even if it is "just a cat", and appears to know Renka and Ryū Genson.
Kaku is a cold, calculative and heartless person who sees his teammates as nothing but mere decoys to be manipulated, stemming from his interrupted execution for disregarding the head's order in the Black Tiger White Dragon clan, during which none of his friends were willing to step in and help him. This heartlessness carries on to his expression, in which he is commonly shown with insane eyes and an eerie smile. However, after being told of the loyalty of his teammates, who pledge never to leave him behind again, he seems to hold a softer spot for them.
Initially, according to Kensei, Kaku hates the Phoenix Alliance because of its thousand year feud with the Black Tiger White Dragon Alliance. This hatred is revealed during his fight with Kenichi to be something more personal, which stems from when Kensei saved him from his death, causing him to be demoted to the lowest rank in the Black Tiger White Dragon Alliance and prevented from committing suicide.
Kaku, along with his teammates Chou and Yo, first arrive at the banquet before the D of D tournament. He ridicules the Shinpaku Alliance during the banquet, and has a maddening obsession with avenging his pride, shown again when his team is set in a battle royale against the Ryozanpaku team.
During the battle, he incorporates his spiraling Tai Ji with Chou's circular Ba Gua and Yo's straight-line Xing Yi, overwhelming and confusing the Ryozanpaku team. He is also able to rearrange the order at will, making it more versatile and capable of damage and confusion. However, his formation is broken when Kenichi and Miu use their combination attacks based on knowing each other's movements. Kaku himself throws his fan at Chou, causing her to be hit by Miu's punch and allowing him to gauge her strength.
This strategy ultimately proves to be useless as he engages Kenichi, who insists on a one on one duel. Kaku proves himself to be a formidable opponent, inflicting grave injuries on Kenichi and comes close of killing him numerous times during the match, using a powerful secret technique called Raisei. He is defeated by Kenichi, who is able to counter his move by using the Taiho Shouha.
Kaku, along with Chou and Yo have left China and the three of them are currently in Japan under the protection of the Ma clan from the assassins sent after them by the Black Tiger White Dragon Alliance. The three work in Uncle Hakubi's Restaurant for minimum wage and to repair the restaurant that was damaged overnight, allowing Renka to transfer to Kenichi's school.