Yu is a bald, muscular man with shadowed eyes and no hair on his face or head.
He wears a dark dress shirt, the top few buttons left undone, and plain pants, along with a pair of black dress shoes. His choice of mask seems to be a simple medical mask that he wears over his mouth, very unlike the signature beak-like mask that’s worn by the rest of the Eight Expendables.
Yu holds a grudge against the people who took advantage of him in the past. He feels abused and considers himself garbage. However, Overhaul gave him a purpose and Yu is prepared to die for his young master. Yu believes that heroes can't understand the bonds between trash like the Eight Expendables.
At some point of his life, Yu had the job of producing gems for an unspecified individual, who planned to sell the minerals for large profits. However, the gems turned out to be worthless, leading to Yu being discarded.
Yu was eventually found by Overhaul in the streets, with the yakuza offering him the opportunity to become his subordinate. With nowhere else to go, Yu accepted and became one of the Eight Expendables.
Yu, Toya Setsuno, and Soramitsu Tabe of the Eight Expendables are tasked with ambushing the Heroes raiding the Shie Hassaikai hideout. Mimic drops a group of the heroes inside a small room where the three villains greet them. Suneater of U.A.'s Big 3 challenges the trio alone.
Yu and Toya launch a preemptive attack on the entire group of heroes, but Eraser Head halts their Quirks and Suneater leaps into action. Suneater restrains the criminal triad and tries to knock them out, but Toya buys them enough times for their Quirks to resurface. Yu immediately activates his Crystallization Quirk and breaks free from his tentacle bonds.
Toya uses his Larceny Quirk to take away Suneater's defense, leaving him open to a crystal-enhanced punch from Hojo. However, the villains underestimate Suneater's resolve and he catches the punch using the maximum output of his Manifest Quirk.  Suneater repels the villains with his Chimera Kraken Super Move and they're forced to make Soramitsu wake up after being knocked out by Eraser Head earlier.
Soramitsu is able to counter Suneater's Quirk by eating his manifested tentacles. Soramitsu and Toya's teamwork leaves Suneater vulnerable to a powerful punch from Yu. When the hero is on the edge of defeat, the three villains explain their past and why they're loyal to Overhaul. Suneater comments that they're just being used and Yu gets angry, claiming a hero will never understand.
Suneater quickly breaks up the villain's teamwork by blinding Toya. He then manifests Yu's own crystals to halt the next attack. Suneater finishes off the villains with a powerful talon and tentacle combination that defeats the Yakuza thugs.
Crystallization (結晶 Kesshō?): Yu's Quirk grants him the ability to produce crystals on his body. This is effective for both close-ranged offense and defense. He can also grow his crystals into the form a sword around his arm.
Handgun: Yu is armed with a pistol, which he uses in combat when his Quirk isn't reliable.
After being deemed useless in his previous job, Yu was discarded on the streets, where he was found by Overhaul. Yu is incredibly loyal to him.