The war between demons and humans ended thanks to the love of the Demon King and the Princess, and peace was brought to the world. Hoping for coexistence between demons and humans, the two set out on a journey to find places where demons could live.

And now 60 years have passed since the Demon King and Princess began living together… On her deathbed, the Princess tells the Demon King, “It was a mistake to let demons out into the world.”. Having lost his beloved wife, the Demon King sets out on a journey. He must face the errors he made, and this time, he must create a world where demons and humans can live together…

(Source: Kodansha, translated)