Moon was the UA traitor.

Sun whimpered and his pupils dilated in fear as Moon held onto his wrists, he could feel them burning from Moon's quirk as he pinned Sun against the wall. "If you tell anyone I'm the fucking traitor, I swear I'll make your life a living hell," Moon growled, his eyes burning with pure fury and anger in his eyes and Sun could feel the intensity of his grip. Sun struggled to break free but it was no use. He were at his mercy. "You're lucky I'm not killing you" Moon hissed