He is Diablo!

In order to realize her dream of a romance with her senpai, Meiko uses black magic. Unexpectedly, she summons the demon king Lucifer, who also ends up as her homeroom teacher!
As part of their contract, Meiko is forced onto the path of a witch, but in reality, she's just Lucifer's slave! And now that she has magical powers, she activates her super strength whenever she eats Anpan. What will become of Meiko and the great demon king Lucifer?