A 20-year-old college student named Wakaba Kayano steps out on Halloween night dressed in her old high school uniform, desperate to reclaim the youthful experiences she never had because she was too focused on studying. She is approached by a boy named Fumito, who is also wearing a high school uniform, and he sweeps her into the perfect movie-like date. When the night is nearly ruined by the revelation of their true ages, they discover a shared secret: Fumito is also a 20-year-old college student, having missed out on his teenage years due to his devotion to basketball.

This embarrassing realization becomes the foundation of their unusual agreement. Rather than ending their charade, they decide to continue meeting in their school uniforms to relive the quintessential high school milestones they both feel they missed. The story follows their escalating attempts to recapture their youth, transforming from a single Halloween escapade into a genuine connection.

The main characters drive this dynamic as a perfect comedic match. Wakaba is an energetic and slightly eccentric daydreamer who is unashamedly enthusiastic about her fanciful romantic expectations. Fumito complements her as a more relaxed and straightforward partner, though with a mischievous streak that allows him to play along with and even encourage her elaborate fantasies. Their chemistry is marked by a lack of unnecessary drama, building instead through humorous and sweet interactions as they navigate pretending to be younger while their real feelings for each other grow.

The narrative unfolds through a series of notable arcs that chronicle their faux-high-school bucket list. After their first Halloween date, they engage in activities like sneaking into their old school at night, which Fumito frames as an infiltration mission just to see her smile. They dive into school festival hijinks, leading to chaotic encounters with the cosplay club, and later progress to more traditional romantic settings like an amusement park. As these self-indulgent fantasies pile up, Wakaba realizes she is catching serious feelings, leading to a central conflict where she must risk their comfortable game to pursue a real relationship before she loses him to someone else. The series culminates over five volumes as they determine whether their belated romance can be just as sweet as the one they dreamed of in high school.