Kouki Terumoto

Koki is traumatized, frightened, lonely, and initially overwhelmed by years of mistreatment.

His family teaches him to regard his own existence as something shameful, leaving him without the emotional support required to understand his Quirk or believe that he deserves ordinary human contact.

After escaping isolation, he becomes increasingly distressed when he sees other people resuming happy lives while he has never experienced comparable security.

His most important characteristic is that he remains reachable. When someone finally approaches him with concern rather than fear, Koki responds emotionally instead of rejecting the connection.

Darkness allows Koki to emit a dark, misty fluid from his fingers and the soles of his feet.

The substance spreads across surrounding surfaces, forming a black or dark-purple field. Objects caught in the affected area sink into it rather than remaining on ordinary solid ground.

When Darkness first manifests, it spreads across an entire room despite Koki's lack of training.

Its full combat potential, maximum area, duration, and weaknesses remain unknown.

Koki is born into a family that reacts badly when Darkness appears as a mutation unrelated to the Quirks known in their bloodline.

Rather than support him, his relatives imprison him and conceal his existence. His mouth is even sewn shut to prevent him from making noise while confined.

The chaos surrounding the Final War eventually leaves him able to escape. Wandering through a society beginning to celebrate recovery, he nearly lashes out with Darkness before an elderly woman takes his hand and tells him she is there to help.

The woman is the same civilian who once failed to help the abandoned Tenko Shimura. Her decision not to repeat that mistake prevents Koki from following a similar path. Eight years later, Koki is shown attending U.A. and training under Izuku Midoriya.

Izuku Midoriya later becomes one of Koki's teachers when he enters U.A.'s Hero Course.

Tenko Shimura never meets Koki, but Koki's circumstances deliberately parallel the neglected childhood that precedes Tenko's transformation into Tomura Shigaraki.

Granny is the elderly woman who finally reaches out to Koki after previously regretting that she failed to help Tenko years earlier.