Sei

A clone of Sora created by Aizawa.

Although he possesses athletic abilities unthinkable for an ordinary person, he was abandoned as a failure by Aizawa because he had no social skills at the time of his discovery. However, after repeated training under Sora's supervision, he was able to acquire age-appropriate (?) social skills.

He is now enrolled in the school as Sora's younger brother and lives in the dormitory where Sora used to live.