Tsubasa

Flashbacks show a round-faced, heavyset boy whose brown hair is clipped down to little more than stubble. Two scarlet wings of a draconic cut unfold from his back whenever he wills them out.

His childhood outfit is simple: a tank top, shorts in green, and geta on his feet.

The series says little about him beyond his conduct as a child, and that conduct was unkind. Alongside Katsuki he made a habit of belittling and roughing up Izuku Midoriya once the latter was declared Quirkless.

He belonged to the small circle of boys, Izuku included, who looked up to Katsuki for seeming to master anything he attempted. Once Explosion manifested, Tsubasa fell in behind him and helped target other children, chief among them the Quirkless Izuku.

He was there for the trip into a forbidden stretch of forest that Katsuki insisted on exploring despite Izuku's reluctance. Katsuki tumbled into the water below, and Izuku's attempt to help him up landed as an insult, setting off years of torment.

The group drifted apart with age, and by middle school neither Katsuki nor Izuku was still in touch with him. His wings carry him in flight, and his name is simply the Japanese word for wing. Since his grandfather turns out to be the man who builds the Nomu, the story hints strongly that Tsubasa became the Winged Nomu.