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.

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 it 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.

With the arrival of autumn, Koguma and Reiko's attention turns to getting ready for winter. When the class culture festival committee runs into a snag getting what they need for their activity, the pair volunteer to use their Cubs to come to the rescue.

Shii invites Koguma and Reiko over to her family's shop for coffee, to allow her father to thank them for their help with the culture festival. The girls continue to look for ways to prepare for riding their Cubs during the upcoming winter months.

With the colder weather taking its toll, Shii comes up with a way to provide both Koguma and Reiko with a little relief. But when the temperature dips even lower, the pair are faced with adopting measures for their Cubs that they are reluctant to accept.

Koguma rushes to the narrow dirt road on her Cub to find Shii, who is half-submerged in a freezing river. She takes her back to her apartment to warm her up and dry her out, but Shii soon reveals that she has other, deeper issues with the winter weather.

The girls pack up and depart on a road trip to Kyushu, the most distant location their Cubs will take them, in order to shake off their winter doldrums and embrace spring. Along the way, Shii finds what she needs to help her continue her café project.

After a snowy night during winter vacation, Reiko invites Koguma over to her house for a surprise. The pair equip their Cubs for the snow, and enjoy a day of fun outside. Shii's father reveals how much of an influence the girls are having on Shii.