Ryuji Ishii attends an academy for those with supernatural abilities. He possesses a pudgy physique, brown hair, and brown eyes. Ishii adhered to a strict daily schedule, maintaining consistent sleep and wake times, and undertook daily jogs aiming for weight loss.

His personality is straight-laced, smart, funny, and exceptionally kind. A skilled comedian popular among his peers, Ishii demonstrated deep loyalty, particularly to his girlfriend, Fuuko Sorano. He consistently declined invitations to social mixers to spend time with her instead. His supernatural ability allows him to shrink his body, potentially down to microscopic sizes like entering pores.

Ishii's background establishes him as Fuuko Sorano's childhood friend and boyfriend. His story reaches its climax when Rentaro Tsurumigawa stabs him outside. Mortally wounded, Ishii requests Fuuko to cut his throat, intending to divert suspicion from her and aid in identifying the real culprit. This occurs in Episode 10, where his body is discovered, prompting an investigation by other students.

His corpse appears in Episode 11. He is later seen in a flashback in Episode 12. His murder profoundly affects Fuuko, who tearfully seeks assistance to avenge him. His relationship with Fuuko and the circumstances of his death contribute to ongoing plot developments, though his direct appearances are limited to these events.