Miumi is a petite, rich high school girl from a super wealthy family. Perhaps because of this, she struggles to make friends. One day, 10 billion yen is bet on Miumi's life, and gangsters from all over the country come after her...!? She is saved by a man in a black sedan, Mikigami Masayoshi, but to her surprise, Mikigami is the young boss of the largest yakuza organization in the Kanto region! He claims that Miumi's parents offered him 10 billion yen to protect her, but in the end, "It's 10 billion yen whether you live or die!" Miumi ends up being held hostage by Mikigami...! And to top it off, the naive Miumi tells Mikigami, who has never cried, "I'll make you cry!"... Yakuza young boss vs. naive high school girl. Who will make her cry, or rather, fall in love? The battle begins, odds are even or even!