Hisui, the Angel Master, and Kokuyo, the son of Satan himself, fell in love one moment between the worlds, at the bridge crossing Heaven and Hell. Kokuyo, self-admittedly a seducer of innocent angels, mistakes Hisui for a innocent angel, and thus... seduces the Angel Master.

Kokuyo makes the sacrifice of one of his obsidian eyes to show Hisui the true depth of his love, and transforms himself from a "player" of sorts, to a devil in a monogamous relationship. Kokuyo is willing to give up his status in Hell and his ties to his father in order to be with Hisui. What could be a greater expression of love?

Hisui, the Angel Master of the Wind, forgoes his powers and his status in Heaven in order to come down to earth to be with Kokuyo. Hisui goes against the angel's inability to eat living things, and even learns to cook (quite well, it turns out!) for Kokuyo! Despite having his Angel Master status revoked, Hisui is able to adapt quite easily to living on earth, and remains quite happy.

This is one of my favorite pairings in the series, because it is so simple and amusing to see. They complement each other, and that's really all that can be said.