Kai Chisaki

Pale and narrow, his auburn hair short and shaggy above a right-side part, his eyes thin over small gold irises. He wears a bomber jacket in dark olive green, its collar thick with purple fur, over a black dress shirt, a pale gray tie, and white sneakers. The white surgical gloves and the magenta plague doctor's mask are what people remember him by, and Izuku Midoriya takes the mask off him.

After the Hassaikai fell he had no arms: Mr. Compress and Tomura Shigaraki removed them with Compress and Decay, and Tartarus left him longer-haired and stubbled with the stumps bandaged. Fused with Shin Nemoto he sprouted a second pair of clawed arms, his mask grafting onto a face wrapped in black fabric. Fused with Rikiya Katsukame his lower half became a stone construct bristling with clawed limbs, his torso seated in its mouth.

He is a mysophobe, an antisocial sociopath, and a man who wants history rolled back to before Quirks existed. An old theory tracing Quirks to rats fed his germ phobia into an ideology: powers are a plague, and heroism and villainy alike are symptoms. Sacrifice and petty crime get the same word out of him, sickness. Erasing Quirks would also hand the yakuza back the grip on society they lost, which is the point. Dirt of any kind brings on hives and takes his composure with it, hence the air-filtering mask on him and on his subordinates. Running the organization he is level-headed and, as Twice observed, pleasant enough on first contact; provoked, a visible killing intent surfaces, and that is the accurate version.

People are inventory. He kills his own men over small mistakes, and their masks remind them they do not deserve his air. Eri, his boss's granddaughter, he took apart and reassembled for her cells, shamed into obedience, and killed her minders in front of her when she got out. He raged when she was taken, and later admitted to Mirio he had never thought of her as his child.

The exception is the old boss, who found him on the street as a child and raised him. That debt is real, and repaying it by restoring the yakuza is the only thing he genuinely wants. When the boss refused him Eri, Kai beat him into a coma and proceeded anyway, telling himself it was for the man's sake. The irony was not lost on Tomura: a plan to erase Quirks that runs entirely on one. Tomura ended it by taking his arms, his Quirk Factor, leaving him Quirkless exactly as he had wanted the world to be. Prison reduced him to a shell mumbling for his boss, wanting no revenge, only to see him again. After the Final War the boss, woken by support technology, visited his cell and named what he had done to Eri, and Kai could only cry and apologize.

Overhaul lets him take apart anything he touches and rebuild it however he likes, which amounts to control over matter. He kills by disassembly and heals by reassembly, does both to himself, and merges with other people to borrow their Quirks, Confession from Shin, Energy Suck from Rikiya. In a fight he reshapes the floor to move himself and drives the terrain up into spikes, which makes every range his. His arms were the Quirk Factor, so losing them ended the power.

Kendo Rappa demanded a fight for his loyalty and was disassembled and reassembled before he could land the punch, and five later attempts went the same way, which says something about Kai's speed given the Quirk needs touch. Lemillion outclassed him until reassembled spikes pinned the hero. Merged with Shin he broke Sir Nighteye and pushed Izuku to 20% of One For All, then, defused by Eri, fused with Rikiya for one last form and lost to Full Cowl at 100%.

The intellect is the dangerous part. Yakuza practice says leave no trail, so he disassembled targets, took what he needed, and restored them intact, leaving no evidence behind. From Eri's Rewind he built the Quirk-Destroying Drug, loaded into red darts, then the blue-capsule serum that reverses it, planning to sell the bullets to villains and the cure to heroes with Eri in the middle and corner the market from both ends.