In Kōchi, Taku Morisaki receives an unexpected call from his friend, Yutaka Matsuno, requesting a meetup at their old high school. Upon arrival, Taku finds Yutaka in the company of the striking new transfer student, Rikako Muto, whom Yutaka has been tasked with showing around. While Rikako excels academically and in sports, her demeanor borders on arrogance, suggesting a deeper unhappiness about her relocation from Tokyo.
During a school trip to Hawaii, Rikako approaches Taku, asking for a loan of ¥60,000 after misplacing her own funds. Though hesitant, Taku, who works part-time, agrees to help her, trusting her promise to repay him while she insists it remains a secret.
As the school year continues in Kōchi, Rikako forms a friendship with Yumi Kohama but has yet to repay Taku, leading him to wonder if she has forgotten about it. Out of nowhere, a panicked Yumi contacts Taku, revealing that she was duped by Rikako into going to the airport under the guise of a concert trip, only to discover their actual destination is Tokyo, using Taku's borrowed money for the tickets. In a hurry, Taku rushes to the airport, ultimately joining Rikako on the trip.
Arriving at her father's residence, they learn that he has moved on to a new relationship, much to Rikako’s dismay. Rikako’s father expresses gratitude to Taku, pays back the loan, and arranges for him to stay at the luxurious Hyatt Regency. Feeling betrayed by her father, Rikako confides in Taku about her past loyalties during her parents' conflicts, revealing her internal struggle. Taku offers kindness by letting Rikako have the bed while he attempts to rest in the bathtub. The next morning, she asks Taku to leave so she can dress for a lunch meeting with a friend.
After a restful day exploring Tokyo, Taku receives an urgent call from Rikako, who needs him to intervene with her former boyfriend, Okada. Upon arriving, Taku's frustration boils over as he chastises them both for their empty discussions.
Once back home, Rikako seemingly ignores Taku but informs her friends that they spent the night together. Yutaka confesses his feelings for Rikako only to face rejection, prompting Taku to confront her during class. This confrontation escalates into an intense argument, resulting in Rikako slapping Taku, who retaliates in frustration.
As the autumn cultural festival approaches, Rikako becomes increasingly isolated, drawing the ire of many peers. Taku witnesses her courage when she stands up to another student, expressing admiration for her strength. However, their interactions remain strained; she slaps him again in a moment of conflict, running away in tears afterwards. Meanwhile, Yutaka, witnessing Rikako's distress, confronts Taku for his lack of support, leading to a rift that isolates them all as they head to different universities.
Years later, Taku, Yutaka, and Yumi reconnect at a class reunion, but Rikako is notably absent. As they reminisce about their high school days, Yutaka reveals his anger towards Taku for holding back his feelings for Rikako, feeling frustrated that a beautiful opportunity was snuffed out due to loyalty. Watching the sunset, they reflect on what might have been.
After the reunion celebration, Taku discovers that Rikako was in Tokyo that day, choosing to forgo the reunion to meet someone who shares her knack for sleeping in bathtubs. Later on, by chance, Taku spots Rikako across a train platform and makes a dash to reach her. Remarkably, she chooses to wait for him instead of boarding the train, hinting that perhaps not all connection is lost.
