Yuuki Rito has had a tough day after once again failing to tell the girl he likes, Sairenji Haruna, how he feels. As he sits and soaks in the bathtub, he gets a shock when the bath water explodes, and from out of the steam comes a girl, who later introduces herself as Lala Satalin Deviluke. From that point, it is revealed that Lala has run away from home due to having to meet marriage candidates on a routine basis. So, to stop this, she announces she will marry Rito, at first to avoid seeing anymore suitors, until she finds herself actually falling in love with the strange earthling. However, the insanity continues onward, as an old fiance appears to try and take Lala away for himself.