Maou Gakuin no Futekigousha: Shijou Saikyou no Maou no Shiso, Tensei shite Shison-tachi no Gakkou e Kayou II - Episode 9

As peace returns to the demon realm, Anos Voldigoad wishes nothing more than to put his reputation as the Demon King of Tyranny to rest and go back to being a misfit at the prestigious Demon King Academy. Unfortunately, any tranquility is fleeting: sinister demons, kings, and deities plot Anos's demise from the shadows. Rumors spread about the "Child of God," a being whose power may rival that of Anos. To uncover the truth and eliminate the potential threat, Anos must journey deep into the land of spirits. However, the spirit world is shrouded in mystery, and it may only be entered after undergoing a series of difficult trials. With unrivaled power and confidence, Anos braces himself to defeat various formidable enemies with grandiose titles. But he—with the assistance of his trusted allies—will barely have to break a sweat as the true Demon King of Tyranny. (Source: MAL Rewrite)