Long after this, Chisaki begins to try to convince Pops of a plan to help restore the Yakuza, which had become almost completely obsolete after the development of quirks. Chisaki suggested using the DNA of Pops' granddaughter, Eri, to formulate a quirk-destroying drug. Eri was chosen because her quirk allows her to rewind people, and this could be used to rewind evolution, thus the appearance of quirks. The plan was for this drug to be distributed in bullets, sold to villains, and then have a cure distributed for those who were affected by the bullets. The end goal was money and infamy, resulting in the reform of the Yakuza.

Pops refused, no matter how much Chisaki tried to convince him. It's unclear what exactly happens next, but it is implied that Kai somehow put Pops in a coma. Afterwards, he takes over the Shie Hassaikai, and begins working to create the drug. The process that was required for that was keeping Eri locked up, scrapping away at her flesh and blood, and reassembling her once she got too tired.

Kai is seen to kill Magne from the League of Villains without remorse after she rushed him. He also disassembled Mister Compress' arm when Compress charged after Magne's death, although this could have just been because Compress touched Chisaki. However, when Chisaki uses his quirk against people when unprovoked, he normally ends up reassembling them afterwards.

Chisaki is mysophobic; he becomes irritated around dust and grime, and when touched he tends to angrily lash out with his quirk. He is shown to express strong distaste towards the mess that disassembling people causes.

Chisaki has a very cold and cruel attitude towards others, viewing everyone around him as pawns. He lacks empathy, and is almost always calm and composed, unless he's touched or in a situation where he's helpless.

In the end, his arrogance and his disregard for others' emotions and friendships would be his downfall. After his base was raided and he was apprehended, the League of Villains worked to crash the vehicle he was in. After taunting him, Shigaraki Tomura and Mister Compress used their quirks to take both of his arms from him. That rendered his quirk useless, and rendered him completely powerless. On top of that, the League also stealed the quirk destroying bullets he had developed, shoving his life's work in his face and revelling in his horror as they leave him to die.

Despite all that happened to him, Kai's status is currently unknown. We can assume that he's either dead or in jail.