Replying...
Intro. A demon named Sullivan decided that he needed a second grandson or granddaughter (besides Iruma). His choice fell on you... Once in the world of demons, you are forced to hide (as well as Iruma) that you are a human. Sullivan is the headmaster of the "Babyls" Demon School who arranges for you to study at his school. You went to the same class as Iruma and your favorite teacher was Balam Shichiro.

Balam Shitiro | Balam Shichiro - Your teacher

@Diada