Sakurai Miu

Miu is a  very innocent 17-year-old girl who has a crush on Amamiya Shion, the most popular boy at school. She hates her child-like body, and prays for being taller, having bigger breasts and of course, for Amamiya's love every day. In her obsession, she casts a spell from an old book, which promises to make every wish come true. However, Satan (the devil) emerges from that book and, in return for his services, Miu has to lose her virginity... and is very afraid of that (as any girl in her right mind would be). But eventually she realizes that she isn't really in love with Amamiya, and falls in love with Satan, giving him his virginity. The problems comes when Sailor, Satan's former lover, gets jealous of her and kills her. Miu ends up in heaven with Amamiya (yes, he was really an angel!), but Satan goes there and "rescues her". In the end Miu decides to become Satan's wife, and their days full of passion start...

Sakurai Kai (Satan)

The attractive and perverted king of all devils, Satan,  emerges from the spells book that Miu uses to make her wishes come true. He has a servant callled Malpas, who is actually a crow. In exchange for his services, he asks for Miu's virginity, saying he doesn't really attention to human concepts of beauty, but to the chance of taking a virgin and pure body. However, when he tries to use his powers on Amamiya, fails, and Satan decides to modify everyone's memory (except for Miu) and becomes Miu's elder brother, Sakurai Kai (and they live in the same house and everything! Imagine how it would be like if you had a incredibly handsome brother who tries to violate you everyday!). While he attempts to achieve his goal, Kai really falls for Miu and starts caring about her. In addition, he develops a strong hatred towards Amamiya. Later, he takes her to a ceremony called "Sabbath" (those events where lust and inmorality reign), and then to hell, but there he re-meets his old lover, Sailor. Nevertheless, he has never felt anything for her, and when she "kills" Miu, Satan finishes her with his own hands. Finally, he defeats Amamiya/Miguel in heaven (but he doesn't kill him) and goes back to hell with Miu, where he promises Miu to take her to human world every now and then (and  make love to her for eternity, that's a given ;D).