An old man is forced to retire from the adventurer's guild and decides to return to his hometown. On his way, he picks up two babies. The first one is a human baby with the emblem of a hero. The second was a baby of the demon tribe with the emblem of the demon king. And so the story of the old man who picked up the hero and the demon king begins.

After being forced to retire from his guild due to his advanced age, adventurer Allen Holder finds two babies with strange birthmarks alone in the forest. One is a prophesized hero chosen to save the world, the other a young demon destined to become the ruler of her demonic brethren. Although the prophecy clearly puts the two infants on opposing sides, Allen raises them side-by-side and treats both of his adopted daughters with love, determined to keep them safe and hidden from those who would exploit their power. But as Lusha and Luna grow older, the outside world begins to encroach on their peaceful lives, demanding they fulfill the roles of their birth. Can Allen protect his children from a destiny that would only bring tragedy to their happy family?