The Demon Sword Master of Excalibur Academy

Leonis Death Magnus, an undead sorcerer and powerful Dark Lord, entered magical stasis during a climactic battle one thousand years ago. When he awakens, he finds a beautiful silver-haired young woman named Riselia standing before him. More shockingly, Leonis has been transformed into a ten-year-old boy! Now he has to adapt to this strange era and deal with the twisted monsters called Voids. All while keeping his true powers a secret from his new guardian.