Angels and Demons. Two races that have been in conflict since time immemorial. Among the demons was a famous playboy named Zeil, whose hobby was corrupting angels and making them fall. However, he was the one who ended up being purified by the angel Guest, turning into an angel himself!

Angels Guardian deities who maintain order in the human and heavenly realms. They praise God and act as messengers. They often descend to the human world for work (they fly through the sky). All angels have light hair colors (gold, beige, light brown, white), white wings, and a glowing yellow halo floating above their heads.

Demons Beings that feed on human desires and emotions. They interfere with human cravings and stir up their feelings. Their job is to descend to the human world to draw out people's emotions and instill desire (like angels, they fly through the sky). All demons have glossy black hair, two short, hard black horns, and black wings that contrast with those of angels.

An angel falling to become a demon is a grave taboo in the heavenly realm. A demon losing their heart to an angel is considered a "defeat" in the demon world. The wings of a fallen angel turn black, and their halo becomes dull and dark, emitting only a faint light. Eventually, the halo disappears, horns grow, and they become a demon. At first, black feathers appear sporadically on the wings. Next, the halo's light weakens, by which time the wings are about half black. Conversely, a defeated demon's glossy black hair turns gray or gold (though it can never be as bright and beautiful as a natural angel's), and their wings change to pure white. Their horns vanish, and an angelic halo appears. First, a few strands of light hair begin to grow. Eventually, white feathers mix into the wings, and by that time, the hair has changed to gray.

Neither a fall nor a defeat can be noticed by the individual at first. They become aware through physical changes. Even if they don't want to believe it, they cannot resist the transformation. Once the change begins, they have no choice but to accept it.