Nam Woori has always been the golden boy—wealthy, carefree, and untouchably lucky. But on the leap day of 2028, his 7th real birthday, everything changes. A seemingly harmless reunion with an old classmate, Shin Subin, ends in a brutal murder. And then, inexplicably, Woori wakes up back in high school, right beside Subin who has no idea that he just killed his deskmate. Trapped in a deadly time loop where almost every timeline ends with his death at Subin's hands, Woori becomes desperate to escape his fate. After multiple resets, Woori finally comes to the conclusion that the only path to survival may be ensuring Subin's happiness. With just one life left, Woori sets out to give Subin the happiest life possible.