Somei Yoshino is a friendly, well-mannered high school girl who lives an entirely normal life – other than the fact that her family is yakuza. However, her peaceful days are thrown into chaos when her grandfather sends her from Osaka to Tokyo in an arranged marriage to Miyama Kirishima, the heir of another yakuza family. Although seemingly polite and even charming at first, claiming not to have any interest in the yakuza life, Kirishima is in reality a violent sociopath who at first dismisses Yoshino for being boring… only to immediately fall head over heels in love with her after she sells one of her kidneys to repay a perceived debt of honor.