Natsuki Haibara is a socially anxious college senior whose high school years were a gray blur of regret and isolation. On the verge of entering the workforce, he finds himself inexplicably transported seven years into the past, landing one month before his first day of high school. Armed with the painful memories of his original timeline and a wealth of adult experience, Natsuki resolves to rewrite his failed adolescence. He launches what he calls the Rainbow-Colored Youth Project, a personal campaign to climb the school social ladder, avoid past humiliations, and finally capture the vibrant青春的 he always dreamed of.

The story is set in a contemporary Japanese high school, where social hierarchies are rigid and first impressions are everything. Having failed his high school debut once before, Natsuki uses his future knowledge to execute a perfect entry strategy. He follows a strict workout regimen, studies online guides for social success, and carefully navigates the complex dynamics of teenage cliques. His calculated approach quickly pays off, allowing him to break into the popular crowd and grow close to Hikari Hoshimiya, the beautiful and admired girl he once only watched from afar. Key figures in his new life include his caring childhood friend, as well as a cast of classmates like Miori Motomiya, Uta Sakura, Tatsuya Nagiura, and Reita Shiratori, whose lives become intertwined with Natsukis second chance.

As the series progresses, Natsukis journey unfolds through several narrative arcs. The early episodes focus on his initial reinvention, carefully orchestrating social encounters and academic achievements to establish his new reputation. However, the story deepens as he realizes that even with foreknowledge, he cannot control every variable. The Rainbow-Colored Youth Project faces unexpected challenges when his actions create unforeseen consequences, altering the lives of those around him in ways he did not anticipate. The central conflict shifts from merely chasing popularity to the ethical dilemma of wielding future knowledge and the struggle to form genuine, unscripted connections. The anime balances lighthearted romantic comedy with introspective drama, following Natsuki as he discovers that a second shot at youth is not just about avoiding mistakes, but about understanding the true value of the moments he is trying to perfect.