Warau Hyouteki

Yuzuru was an average teenager who had almost forgotten that he was betrothed to Azusa when he was only 6! Now arriving to claim what she feels is rightfully hers, only Satomi (Yuzuru's current girl friend) stands in her way... and with the mysterious and frightening powers that Azusa brings, Satomi won't stand in her way for long!

(Source: AniDB)