Eri

A small brown horn juts from the right side of Eri's forehead and swells whenever Rewind engages. She is slight, with enormous red eyes and pale bluish-white hair parted at the center that falls nearly to her waist, tangled and untended through her early appearances. She first turns up in a grubby tan shift, arms and legs wound in bandages that hide a map of scars.

Life at U.A. replaces that with a frilled white blouse under a plain red pinafore fastened by two oversized gold buttons, gray tights, boots several sizes too big, and a dark red satchel worn on the right shoulder with a pair of flowers on its side. Her hair, finally cared for, hangs straight. Late in the Final War she had Ectoplasm help her break a piece off her own horn and handed it to Shota Aizawa so Izuku could be saved. Eight years later the horn has healed and grown out longer, and she wears a school seifuku with red trim double-lined in white, a blue scarf, dark brown leggings, and a guitar case on her back.

Her mother cast her out after she accidentally erased her father, and Kai Chisaki's experiments finished the job of teaching her she was a weapon and nothing else. What emerged was a child who did not scream when someone meant to hurt her, because she had concluded that whatever happened to her was simply owed. Izuku's hand on her was, as far as she could tell, the first kindness of her life, and it made her cry. She kept trying to run from her captors anyway, with nowhere to run to.

Chisaki's real damage was moral. Convinced her existence injured people, she was willing to walk back to him rather than let anyone bleed for her. Even after the rescue she could not manage a smile, having no template for one, until Class 1-A's band played the U.A. School Festival and something finally landed. The Quirk stayed a source of shame too, until Izuku's insistence that Rewind could do good turned her toward training it, and the proof came when she handed Mirio Togata his Permeation back, tearful and telling him to stop apologizing, since she had been practicing precisely to thank him.

Kyoka Jiro's turn as the band's singer struck her hardest, and she decided she wanted to sing too. When the war ended she got her performance, with Kyoka on lead guitar behind her. Eight years on she is a thoughtful, warm middle schooler who enjoys music with her classmates, credits Shino Sosaki and Kota Izumi with taking her in, and admires Izuku and Mirio without wanting to trade on their fame. Gaps remain in ordinary things; she once filed Halloween, Setsubun, and Easter all under Christmas.

The Shie Hassaikai's boss is her grandfather, and her blood was the engine of Kai Chisaki's Quirk-Destroying Drug operation. Rewind reverses a living body toward an earlier state, making a target physically younger, closing wounds, or undoing modifications, and taken far enough it can wind someone back past the point they existed at all. Her father went that way when the power first surfaced. The horn holds the source, its size setting the strength, and Neito Monoma's copy revealed that the power accumulates over a period before it can be spent. Because the mutation runs through her body, her blood can strike a Quirk itself and stop it activating, which is exactly what Chisaki harvested by taking her apart and reassembling her.

She had no education in any of it. During the Shie Hassaikai Raid she first felt the shape of it when she pulled Chisaki and Shin Nemoto out of their fusion, and in Izuku's fight with Overhaul she stored enough to push him to Full Cowl at 100 percent, then could not stop, rewinding him toward oblivion until Shota Aizawa's Erasure cut it off. Izuku and Mirio's rescue brought her a home in the U.A. dormitories and staff willing to teach her, and she worked up from regrowing the limbs of insects and lizards to restoring Mirio's Permeation on the eve of the Paranormal Liberation War.

Eraser Head believed Rewind might restore lost Quirks generally, while noting its hard limits: it touches people, not objects, and it certainly cannot be pointed at time, which is not alive. In the Final War she snapped her horn off herself; detached, it still worked, spending the two or three minutes of charge she had banked to bring Izuku's arms back. Guardianship passed from her grandfather to Mandalay afterward, putting her in a home alongside Kota Izumi and pointing her at a career in music and starting to busk under Kyoka's coaching.