One is a goddess in the fairy world, and the other is a devil in the devil world. Thousands of years of duels have slowly changed the relationship between the two from enemies to love.
However, the devil only shows love on a whim, while the fairy gives his true love.
This love between gods and demons began quietly, but also ended quietly, and their children, a son of god who was originally unrivaled in the fairy world, and a successor to the demon world, were changed by their mother, just for their own wishes.
Because of her single obsession, it caused an inescapable disaster...