A thousand-year-old Dark Lord wakes up as a kid and has to pretend to be harmless while the most powerful magic in his body screams to get out. The comedy comes from watching him fail at being a normal student, fail harder at hiding what he is, and fail completely at not falling for the woman who's supposed to be watching him. It's a show that knows exactly what it is: the setup for a romance that shouldn't work but does because neither of them can stop being themselves.

Leonis Death Magnus, the undead Dark Lord who outlasted all his peers, wakes from a thousand-year stasis to find himself in the body of a ten-year-old boy. Standing over him is Riselia, a silver-haired girl who becomes his guardian in this unfamiliar new world. Sorcery has given way to magical devices, and the war that defeated him has been forgotten. Humanity now faces the Voids, monstrous creatures that have nearly wiped it out. Riselia assumes he has lost his memory and enrolls him at Excalibur Academy, where students who wield Holy Swords train to fight the Voids. Leonis still means to conquer the world, but first he must adapt to this changed era while keeping his true power hidden from the girl looking after him.