The world is split into two realms: the Kingdom of White, floating in the skies under Queen Iris's rule, and the Kingdom of Black, resting on barren lands below and governed by the King of Darkness. Recently, evil forces have gathered significant strength, endangering the entire world. As the primary embodiment of Light, Iris must uphold the world's balance and repel the darkness threatening her kingdom. Meanwhile, in the Kingdom of Black, rampaging monsters destroy a specific boy's village, leaving him as the only survivor. While he mourns in despair, an armored man named Skeer spots the child and offers comfort. Shortly thereafter, Skeer perceives the boy's potential to alter the kingdom's status quo and names him his heir before dying. The boy then pledges to become the Prince of Darkness—the successor to the King—to restore the world to its proper course. As Iris and the Prince of Darkness each confront the looming catastrophe in their own ways, their fates will intersect, and perhaps their connection will determine the world's destiny.