Yumi Kohama attends the same Kōchi high school as Taku Morisaki and Yutaka Matsuno. She forms a close friendship with transfer student Rikako Muto after Rikako faces difficulties adjusting socially following her move from Tokyo. This bond makes Yumi Rikako's primary confidante among their peers. In their third year, Rikako lures Yumi to the airport under false pretenses of attending a concert. Yumi discovers Rikako's real intention is to travel to Tokyo using money borrowed from Taku. Stunned by the deception and the situation, Yumi contacts Taku for help. Taku intervenes, sending Yumi home while he accompanies Rikako to Tokyo. After graduation, Yumi attends a class reunion with Taku and Yutaka. She tells Taku about a recent meeting with Rikako, relaying Rikako's reason for missing the reunion: Rikako went to Tokyo hoping to meet "someone who sleeps in bathtubs," an indirect reference to Taku based on their shared history. During the reunion gathering, classmate Tadashi Yamao emotionally confesses his romantic feelings for Yumi.