Shinta Sato is a rookie police officer driven by a strong sense of justice. While trying to stop a runaway car from crashing into a line of children, a collision knocks him unconscious. He awakens to find himself transported thirteen years into the past, back to his high school days. The date is the very day his best friend, Masaki, took his own life. Despite knowing what is about to happen, Shinta finds that he cannot alter fate, and his friend dies again before his eyes.

Consumed by grief, Shinta attends the funeral, something he failed to do the first time. There, he uncovers a devastating truth, Masaki had been the victim of relentless and brutal bullying. As a police officer, Shinta knows the proper channels for justice, but the raw emotional impact of seeing his friend's suffering leaves him questioning his purpose for being sent back. He soon realizes that a mysterious firearm has traveled through time with him. Clutching the gun, a dark and determined resolve begins to grow within him. He decides not only to prevent the tragedy but to exact a violent revenge on those who drove his friend to despair.

The story is set in a contemporary Japan that is forced to confront its deep social traumas regarding bullying and institutional silence. The narrative quickly escalates from a mission of rescue into a dark vengeance noir. Shinta uses his future knowledge and his weapon to confront the aggressors. In one pivotal moment, he fires the gun at one of the bullies, crossing a definitive moral threshold. This act transforms his quest from saving a life into a complex psychological dilemma, forcing him to question if he is still a hero or if he has already lost himself to the cycle of violence.

As the story progresses, Shinta survives a narrow escape from a gang only to face even more relentless pursuit from vicious siblings known as the Sasaki brothers. Other key figures emerge, such as his future boss, Futaba-san, whose connection to the past adds layers of mystery. With only two bullets remaining and past and present violently colliding, the full truth behind Masaki’s death begins to surface in what is described as the shocking true chapter of this time-traveling saga.