Kurumi Sahana arrives as a mysterious transfer student and quickly becomes the most enigmatic presence at the center of the story. Her background is shrouded in deliberate ambiguity, with only sparse hints emerging about her past. It is suggested that her parents are deceased and that she spent part of her childhood in an orphanage alongside her siblings. She lives alone, a secret she shares only with Hideo, and her circumstances remain largely hidden from others. Physically, she presents a frail frame, short black hair, and a small bust, yet her understated appearance belies a personality of stark contrasts.

On the surface, Kurumi is quiet and self-contained, often wearing an expression so subtle that only Hideo learns to read it accurately. She projects an air of naivety, but this masks a keen awareness of the attraction Hideo feels for her and a calculating mind that asserts control over their dynamic. She positions herself as his master, orchestrating a transactional relationship in which she guides his behavior through a system of psychological and physical rewards and denials. Her most notorious act is to push Hideo to the brink of sexual release only to stop just before the moment, a practice that embodies the very meaning of the title. This teasing cruelty is not simple sadism; it is a method by which she forces him to confront his own weaknesses, build endurance, and grow beyond his initial cowardice and lack of ambition.

As the narrative progresses, cracks in the femme fatale persona begin to show. She is occasionally seen with medicine bottles and suffers from sudden bouts of fatigue, gradually revealing a deeper tragedy. Kurumi’s true motivation becomes the urgent desire to leave a lasting mark on Hideo’s life and to be remembered after she is gone. Her actions are less about amusement and more about teaching him how to endure longing, how to become strong in the face of deprivation, and how to love without relying on physical gratification. She becomes the catalyst for Hideo’s entire transformation, pushing him to jog, to improve his physical strength, and to stand up for himself in ways he never would have otherwise.

Her key relationship is with Hideo Aiba, the protagonist and president of the Roman club. She joins that club explicitly to be near him, and from that point forward their lives entwine in a charged, often painful intimacy. While their bond can appear one-sided and manipulative, it is underpinned by a profound emotional connection that transcends the physical games they play. Outside of Hideo, her interactions with other characters are selective. She initially draws hostility from Kyouko, a brash and popular girl, but gradually a form of friendship develops between them. The Roman club members observe her with a mix of curiosity and wariness, never fully grasping the depths of her hidden suffering.

Kurumi’s development throughout the story is a slow unveiling. Early chapters frame her as an almost mythical, unreadable figure who seems to toy with Hideo for her own enjoyment. Later, the revelation of her deteriorating health recontextualizes every previous interaction, casting them as desperate attempts to prepare the boy she loves for a world without her. Her ability to maintain control while carrying a terminal secret becomes her most remarkable trait. She does not possess supernatural powers, but her skills are psychological: an uncanny ability to manipulate desire, to read and shape Hideo’s emotions, and to use restraint as both a weapon and a lesson. By the end, the reader understands that her teasing was never cruelty for its own sake, but the painful methodology of a young woman who wanted to teach someone how to stand on his own before she inevitably faded from his life.