Shinichiro Niihama is a thirty-year-old man broken by years of grinding work at an exploitative company. After collapsing from exhaustion on the job, he wakes up in the body of his high school sophomore self, fourteen years in the past. His mother, who had died in his original timeline, is alive again. Retaining all his adult memories and the hardened endurance he developed as a corporate slave, Shinichiro resolves to take revenge on his wasted youth. He sets two primary goals: to study hard enough to escape the dead-end career path that destroyed him, and to save Haruka Shijouin, the beautiful and kind girl he pined for from afar. In his original life, Haruka was driven to suicide at age twenty-five after enduring relentless bullying at her own workplace. Now, Shinichiro volunteers alongside her as a library assistant, using his adult perspective to offer her subtle guidance and support. His mature confidence allows him to stand up to bullies without fear, and his unexpected competence begins to shift his social standing from the bottom of the hierarchy to somewhere much higher. As Shinichiro gently steers Haruka away from the isolation and self-doubt that led to her tragic fate, she grows increasingly curious about the changed version of the quiet boy she remembers. Meanwhile, his younger sister Kanako cheerfully pushes him to pursue a real romance rather than remain a vague protector. The story unfolds as a warm, second-chance romance built on the contrast between adult weariness and adolescent innocence, with each small success in the present rewriting a future that was once written in sorrow.