Sonoda Kanna, a promiscuous girl, has a one-night stand with a woman named Amagi Mikage-only to discover that Mikage is the heiress of the Amagi group, a Yakuza group! With no memory of the previous night, Kanna is stunned when Mikage suddenly declares- completely unilaterally-that they're getting married. Trying to escape from the serious Mikage and the yakuza members, Kanna soon finds herself getting dragged into a succession struggle within the syndicate...