Natsumi is still in the process of recovering from the death of her beloved younger sister, Haru. However, she has been secretly dating Tougo, Haru's fiancé. Even though their engagement was arranged for convenience, Natsumi knows that Haru truly loved Tougo. Despite this, she agreed to date Tougo under the condition that he takes her to all the places he went with Haru.
Although Natsumi feels ashamed, she meets Tougo every week to visit the places he and Haru went to and listens to his stories. After an emotionally painful encounter, Natsumi decides to end her life by moving in front of a moving train, but Tougo stops her by announcing that he will die too if she goes through with it.
As the seasons change from spring to summer, Natsumi and Tougo, two people united by grief, find comfort in each other's company. They struggle with their own emotions while cherishing the memory of their departed loved one.
