Soi is a lean, tall demon who has a bowl-cut style of white-colored hair. He also has a pair of miniature-sized black horns and pointy ears on his head. His skin tone is very light. At a glance and when mostly seen, Soi is quiet and doesn't really talk to his classmates. His mouth is never seen to open, with their eyes expressing a blank state, and his face has always looked bland and gloomy, as if he's always bored. He often turns his head to one side or the other when he appears.