Yoshioka-sempai attends the same high school as Atsumi Miyagawa, where he commands attention as the basketball team's star player, celebrated for his athletic skill. Despite this prominence, he openly identifies with a lolicon fetish, actively seeking and evaluating girls he perceives as having "loli" qualities. His fixation centers intensely on Atsumi, whom he labels a "legal loli" due to her childlike appearance despite her high school age, driving persistent advances toward her at school.

Alarmed by Yoshioka's inclinations, fellow student Makoto Kobayashi deliberately engineers a relationship between him and Atsumi. Makoto aims to provide a socially acceptable outlet for Yoshioka's preferences, hoping to deter him from pursuing underage girls and facing legal repercussions. Yoshioka's obsessions directly influence his behavior and athletic performance; his motivation and prowess on the basketball court surge dramatically when "inspired" by individuals matching his fetish, even when aware of their actual age.

He shares a contrasting dynamic with his older brother, who exhibits a pronounced attraction to significantly older women—a preference that unsettles characters like policewoman Miura. Within the series' third season, Yoshioka acts as a catalyst for comedic scenarios, propelling plot developments through his pursuit of Atsumi and distinct quirks. This shifts narrative focus toward Atsumi and introduces fresh dynamics among the characters.