Futaba Yoshioka (Natsuki Deguchi) and Kou Mabuchi (Kaede Sakurai) gradually draw closer to each other's feelings and come into close contact on the day of the cultural festival. Futaba, who wants to know Kou's true feelings, resolves to convey her feelings to him. Just then, Yui Narumi (Karin Fujiyoshi), a classmate Kou met in Nagasaki when he transferred during middle school and who shares the same sadness, appears before them. Unable to leave Yui, who knows the same sadness, alone, Kou embraces her in front of Futaba and Toma Kikuchi (Ryosuke Sota). Their youth is just one millimeter away, yet so distant.

Futaba's heart sways greatly at Toma's straightforward words, and the distance between them rapidly closes. Meanwhile, as Kou recalls painful memories with his mother, Akari (Keiko Horiuchi), he once again realizes his feelings for Futaba. Encouraged by Aya Kominato (Yasutaka Niibata), Kou decides to face his honest feelings and meet Yui again to sever any lingering emotions of sympathy. In the midst of this, Toma presses Futaba for an answer to his confession. What answer will Futaba come up with?

Futaba has started dating Toma. Meanwhile, the time for the school trip is approaching. Coincidentally, the destination is Nagasaki, where Kou spent his final days with Akari. Witnessing the intimate relationship between Futaba and Toma, Kou feels uncomfortable. On the other hand, developments begin to unfold in the relationships between Shuko and Kominato, Makita Yuriko (Riko) and Naigu Haruhiko (Miyazato Soru). Kou decides to take action to create new memories in Nagasaki.

Despite feeling bewildered by Kou's invitation, Futaba decides to accompany him as a representative of their friends. Kou tries to move forward to overcome his sadness as they walk through the streets of Nagasaki. Futaba's heart wavers as she tries to support Kou, but she begins to feel guilty towards Toma. Later, Futaba honestly tells Toma about sneaking out with Kou during the school trip and promises to face their issues together. On the other hand, Kou, in an attempt to establish boundaries with Yui, meets with her—.

Unable to erase Kou from her heart, Futaba heads to Toma to bid farewell. However, Kou, without knowing about Futaba's decision, stops himself from reaching out to her. Futaba and Kou continue to pass by each other... And then comes the Christmas night. Amidst the intertwining of their feelings, Futaba visits the place filled with memories of Kou. Over and over again, it felt like it would start but never did, between Futaba and Kou. Near yet far, will their youth, just one millimeter away, truly reach its conclusion?