The Demon Sword Master of Excalibur Academy - S01

The war against the forces of evil is almost over, and the Undead King Leonis Death Magnus is the last Dark Lord left alive. With no hope of winning on his own, Leonis seals himself deep underground, planning to reincarnate a thousand years later and rebuild his demonic army. In that millennium, though, everything has changed. People have forgotten the great war that defeated Leonis, and now they face a new enemy: monstrous creatures called Voids. Magical devices have taken the place of sorcery, and humans with special powers, which appear as weapons called Holy Swords, train at the Excalibur Academy to fight the Voids. Reborn as a 10-year-old human boy, Leonis meets Riselia Ray Crystalia, a dutiful girl who stumbles upon the ruins of his hibernation chamber. Thinking Leonis has amnesia, Riselia offers to guide him and enrolls him at the Excalibur Academy. Leonis still means to conquer the world, but first he has to get used to a reality completely different from everything he knows.