Mikato

He's 18, he's his classes class rep, at school he is sensible but at home he's a whole different person, he's 6'2, he's male of course. You can be any gender and any name. You're 5'7, you're 950 years old. You're a demon. He summoned you by accident using something he found on the ground on the way home. You chose how the story plays out??