A salaryman named Ibuki Doi has never been able to forget his first love from high school, Mikami Baba. Mikami was the kind, handsome, and seemingly straight student council president, and Ibuki was too shy to ever approach him. Years later, while scrolling online, Ibuki is devastated to learn that Mikami is engaged to be married to another man. He drinks himself into a stupor to drown his sorrows but wakes up to find himself inexplicably transported back in time to his own high school days. Realizing he has been given an impossible second chance, he resolves to do things differently and finally get close to the boy he has always loved.

The story takes place in contemporary Japan, shifting between the present day where Ibuki is an adult and the past when he and Mikami were classmates. The central conflict deepens when Ibuki remembers a dark chapter from Mikamis past: the murder of his older sister, Mikoto, by a neighbor. The tragedy caused Mikamis family to move to America, a painful separation that Ibuki now has the chance to prevent. Gathering his courage, Ibuki reveals his secret to Mikami, confessing that he has come from the future specifically to save Mikotos life. Remarkably, Mikami believes him, and the two form an unlikely alliance to change the course of history.

This collaboration brings them closer than Ibuki ever dreamed possible. As they work together, the fateful day arrives and passes without incident. It appears their plan has succeeded, and the timeline has been altered. In a moment of pure happiness, Mikami kisses Ibuki and suggests they try a serious relationship. However, this joy is short-lived. Soon after, Mikami begins to inexplicably distance himself, leaving Ibuki confused and heartbroken. Meanwhile, the ripple effects of their actions begin to surface. A man named Noah, who in the original timeline was Mikamis husband, appears in Japan, and Ibuki is forced to confront the unsettling possibility that in saving Mikotos life, he may have erased the other future where Mikami found happiness.

Throughout the story, Ibuki struggles with anxiety about the uncertain future and the fragility of the new present he is trying to build. The narrative follows his journey from a passive, regret-filled adult to a young man actively fighting for the life he wants. For his part, Mikami must navigate the unbelievable truth about the time leap while dealing with his growing feelings for Ibuki and the heavy burden of trying to protect his family. In the end, the story resolves the central mystery of the time leap and the fate of Mikamis sister, forcing both characters to accept the consequences of their choices and define what a second chance truly means for their relationship.