Kai Chisaki, alias Overhaul, leads the Shie Hassaikai yakuza. His pale skin, narrow frame, short auburn hair, and thin gold-irised eyes are distinctive, along with a small scar on his left forehead from a clash with the League of Villains. He typically wears a magenta plague doctor mask with gold accents—functioning as an air filter due to severe mysophobia—white surgical gloves, a dark olive-green bomber jacket with purple fur trim, and formal black attire beneath. Following his defeat, he lost both arms, permanently disabling his Quirk, and later appeared in prison with longer hair and stubble. Orphaned young, Chisaki resided in a facility run by All For One's associate, Kyudai Garaki. There he encountered a theory proposing Quirks originated from a rat-borne virus, solidifying his belief that Quirks are a societal disease. Rescued from the streets by the Shie Hassaikai boss, Chisaki developed deep loyalty, viewing the boss as a father figure and feeling indebted. This debt fueled his obsession to restore the yakuza's prominence, diminished by Quirks. Even in childhood, he violently defended the yakuza's honor, despite the boss discouraging such brutality. Chisaki wields the Quirk "Overhaul," enabling him to disassemble and reassemble any matter he touches, including living organisms, inorganic materials, and himself. He can fuse with others, absorbing their Quirks, as demonstrated by merging with subordinate Shin Nemoto to gain limbs and claws and Rikiya Katsukame to form a massive stone construct. His combat style leverages environmental manipulation, creating spikes or terrain advantages. The loss of his arms permanently prevents Quirk activation. His germophobia triggers physical hives upon contact with contaminants like blood or dirt, intensifying his disdain for human interaction. He perceives society as infected by "Hero Syndrome" and villainy, blaming Quirks as the root cause, despite relying on his own power. He exhibits no regard for human life outside his boss, treating individuals, including subordinates, as expendable tools—killing underlings for minor failures and enforcing compliance through intimidation. Chisaki fixated on Eri, the boss's granddaughter, due to her unique "Rewind" Quirk, capable of reversing biological states. He conducted brutal experiments on her, repeatedly disassembling and reassembling her body to harvest blood cells for Quirk-Destroying Bullets. These bullets temporarily suppressed Quirks, with Chisaki aiming for a permanent version. He psychologically manipulated Eri, blaming her for his actions and isolating her to ensure compliance. His plan involved monopolizing the bullets and their antidote to control the underworld and hero society. Initially allying with the League of Villains to exploit their influence, Chisaki killed Magne and severed Mr. Compress's arm during negotiations, citing their "unclean" contact and igniting lasting enmity with Tomura Shigaraki. When Eri briefly escaped, Chisaki encountered heroes Izuku Midoriya and Mirio Togata, posing as her father. He later killed the subordinate responsible for her escape. During the Shie Hassaikai raid, Chisaki fused with Nemoto and Katsukame to battle Midoriya. Eri's uncontrolled Rewind Quirk separated the fusions and healed Midoriya's injuries. Midoriya ultimately defeated Chisaki, destroying his mask. After arrest, the League ambushed his transport, stole the Quirk-Destroying Bullets, and Shigaraki decayed his arms as retribution for Magne. Unable to heal his comatose boss, Chisaki descended into despair. Imprisoned in Tartarus, Chisaki sank into near-catatonic depression, fixated solely on apologizing to his boss. During a prison break orchestrated by All For One, Lady Nagant freed him; he bargained with Midoriya to see the boss in exchange for reconciling with Eri. Post-war medical technology revived the boss, who visited Chisaki in prison. The boss condemned his actions, particularly toward Eri, prompting Chisaki to weep and apologize repeatedly. The boss vowed to remain at his side, ensuring Chisaki atoned for his crimes indefinitely.