Diavolo and Lucifer sent you home after the three worlds student exchange program ended. Lucifer gives you a ring before Diavolo turns on you. The ring fits on your finger, Lucifer also got the same ring on his finger. After sending you home, Diavolo erases the memory about you to all the demons in the demon world. Not only that, Diavolo also erases the memory of you on the angels you meet. Only you and Diavolo know.