The character in question is Hideo Aiba, the main protagonist and narrator of the story. He is a fifteen-year-old high school student who serves as the president of the school's Roman Club, an organization nominally dedicated to investigating paranormal phenomena like ghosts and UFOs. Physically, Hideo is described as having a small build and short black hair. At the outset, he lacks both physical strength and personal bravery, presenting as a somewhat timid and unremarkable young man.

Hideo's personality and motivations are deeply intertwined with his complex relationship with Kurumi Sahana, a mysterious transfer student who joins the Roman Club. He becomes her self-described "voluntary plaything," driven by powerful feelings of attraction and devotion to her. Kurumi establishes a system of rewards and punishments to shape Hideo's behavior. He agrees to perform whatever tasks she demands, no matter how humiliating or difficult, in exchange for her approval or a promised reward. This dynamic becomes the primary engine for his personal growth.

The intense jealousy Hideo feels when other men interact with or grope Kurumi fuels his desire for self-improvement. He fears being unable to afford gifts for her and feels inadequate compared to his rivals. To cope with his frustration and win Kurumi's regard, Hideo commits to a rigorous regimen of jogging and physical training. This dedication yields tangible results, as his physical strength and endurance gradually increase over the course of the narrative. His commitment is such that he endures severe physical discomfort, including resisting a judo arm-bar from the school's martial arts champion, simply to earn a "reward" from her.

Hideo's role in the story is to undergo a transformative arc, evolving from a cowardly, lack-luster boy into someone more disciplined and resilient. His entire identity is shaped by his submissive yet deeply affectionate relationship with Kurumi, who acts as both his "master" and the object of his affections. While his fellow club members serve as comic relief and observers, Hideo's journey is the central focus, chronicling how his transactional relationship with Kurumi forces him to confront his own weaknesses and strive for a better version of himself. His notable abilities are not supernatural but are grounded in his newfound willpower and physical conditioning, enabling him to perform feats of endurance he would have previously been incapable of achieving.