Kei Takato, an ordinary university student searching for part-time work, receives an irresistible offer: to act as a mathematics tutor for his professor's niece, Yukari Fujioka, twice a week and for ten thousand yen per hour. Taken aback by this lucrative deal, Kei accepts.

Young, cute, and baby-faced, Yukari is an alluring girl. Little do people know, she is also a high school dropout who has amassed a gargantuan fortune of 170 billion yen through the stock market. However, despite her immense wealth, Yukari lacks friends and real-life experiences; it is up to Kei to save her from solitude, all while managing his own growing feelings.