Koguma, a shy 2nd-year student in high school with no parents, no money, no friends, and no goals for the future decides one day to shop for a motorbike. When she buys an inexpensive used Honda Super Cub, it leads to events that will change her life.

When Koguma lets in slip in class that she owns a motorbike, she attracts the attention of Reiko, one of the girls who sits near her. Reiko insists on seeing Koguma's Cub, as well as showing off her own, and is pleased to meet a fellow Cub rider.

As Koguma slowly adjusts to life with her Cub, she mentions to Reiko that her luggage case seems convenient, so Reiko makes a call. After school, the pair visit a credit union, where the manager has an old Cub with a luggage case available to them.

With summer vacation approaching, Koguma plans to spend it working for the school, shuttling papers back and forth to a high school in Kofu. Along the way, she finds herself learning more about maintaining her Cub, and the perils of inclement weather.

Koguma visits Reiko at her home, and the two have dinner together. Reiko recounts the story of how she took a job at the Mountain Hut Kikuya over the summer as a means to pursue her own dream, something which proved to be more difficult than expected.

The night before the class excursion to Kamakura, Koguma comes down with a fever, and must cancel. The next morning, after her fever is gone, she makes the bold decision to hop on her Cub and set out on the long journey to catch up to her class.