At the age of 5, Keitaro made a promise with a girl that they would both go to Tokyo U (Tokyo University) and be together forever. That little girl moved away, and 15 years later, all he can remember about her is the promise they made. Wanting to keep his promise, Keitaro continues to aim for Tokyo U, even after failing the entrance exam two years in a row.
Not being able to support himself, Keitaro goes to stay with his grandmother at the Hinata Hot Springs, which used to be an inn, but to Keitaro's surprise, is now an all-girls dormitory. This leads to some very awkward encounters with the Hinata residents, including Naru Narusegawa.
Thinking Keitaro is already a Tokyo U student, and the dorm in need of a manager, Keitaro is allowed to stay at the Hinata Apartments. But not without many reservations by most of the girls in the dorm. Things only get worse when it is discovered that Keitaro is not actually a Tokyo U student, and fails the entrance exam for a third time.
Still, Keitaro is allowed to stay, where he can continue to study and work as apartment manager.