In order to protect the girl Yuuhi Katagiri, a new transfer student, from danger, Junichi Nagase is forced to kiss her. Not understanding what happend, she screams at him, not knowing that her father has arranged for her to marry him

One day Junichi Nagase comes across two boys tormenting Yuuhi Katagiri. When he steps in to help they run off calling him "Geno Killer". He then walks off without introducing himself or allowing the girl to either. The next day to both of their surprise she is introduced as a new transfer student to his class. The following day due to a misunderstanding he kisses her which greatly upsets her. That evening to his surprise and dismay she shows up to his door saying she is his fiancée and that she has come to live with him to evaluate him to see if he is worthy of her. Much hi-jinx ensues as the days go by.

One day Junichi Nagase, once a savage delinquent known as the "Geno Killer", saves Yuuhi Katagiri from danger. Later Junichi finds out that Yuuhi is a transfer student who has come to evaluate him as her fiance in an arranged marriage, and begins living with him and his sister, Minato.