Jun'ichi Nagase attends a prestigious high school. He has the nickname Geno Killer since he was rebellious in middle school. This is used, inadvertently, to help a girl named Yuuhi Katagiri from trouble. She later transfers to his school. Jun'ichi then kisses her due to a misunderstanding. Outraged, because he stole her first kiss and embarrassed her, she screams at him. Subsequently, it turns out that Yuuhi is his fiancé as arranged by their parents. Their parents discuss the matter and order them to go out together for a month to restore their relationship. If their relationship does not get better, the engagement will then be cancelled.