One thousand years ago, Leonis Death Magnus, undead sorcerer and the greatest of the Dark Lords, entered magical stasis during a climactic battle. 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'll have to adapt to this strange era and deal with the twisted monsters called Voids—all while keeping his true powers a secret from his lovely new guardian. 
 
(Source: Yen Press) 
 
Note: Each episode streamed 1 week early on ABEMA. The original TV broadcast started on October 3rd, 2023.

One thousand years ago, Leonis Death Magnus, undead sorcerer and the greatest of the Dark Lords, entered magical stasis during a climactic battle. 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’ll have to adapt to this strange era and deal with the twisted monsters called Voids-all while keeping his true powers a secret from his lovely new guardian.
 
(Source: Yen Press)

One of the most powerful demon lords in history has been sealed away for a thousand years. When he finally awakens, he is reincarnated as...a 10-year-old boy?! Now under the care of the girl who released him, the demon lord Leonis must navigate the perils of Excalibur Academy!
 (Source: Yen Press)

Blackas Shadow Prince