Kazuhiko Nukumizu is the main protagonist and viewpoint character of the series. He is a first-year student at Tsuwabuki High School, initially in Class 1-C, who later becomes the president of the school's Literature Club after taking on the role to support a fellow member in a difficult situation.

In terms of appearance, Kazuhiko is a teenage boy of average height and a very average-looking face, which contributes to his unassuming presence. He has black hair, dark brown eyes, and fair skin. His typical school attire is the standard Tsuwabuki High uniform. Outside of school, he has a notably terrible fashion sense, often choosing clothes that are out of date or gaudy because he personally thinks they look cool. His build is described as slender, and he is capable of successfully cross-dressing with some adjustments.

Kazuhiko's personality is defined by his self-identification as a loner who prefers reading to social interactions. At the beginning of the story, he has no friends and can come across as cold and unapproachable, leading others to have misconceptions about him. He has a habit of saying unnecessary things and being bluntly honest, due to his lack of social experience, though this bluntness often turns into wordy excuses when he gets nervous. Despite his struggles with people his own age, particularly the opposite sex, he has no problem dealing with those younger or older than him.

He is a massive otaku, with a collection of merchandise like light novels, posters, and dakimakuras adorning his room. He has zero experience and little interest in romantic relationships, believing that love is not for him while also admitting he is still attracted to girls. A significant part of his personality stems from taking care of his younger sister, Kaju. This has made him severely overprotective of her, leading others to jokingly call him a siscon, a label he denies. Because he is used to spoiling his sister, he often treats the girls around him in a similar manner, making them feel very comfortable in his presence.

Despite his social ineptitude, Kazuhiko is quite mature for his age. He has a strong sense of responsibility, exemplified when he becomes club president to save another student from a humiliating situation and when he takes the blame for a confiscated doujinshi that he did not write. While he prefers not to stick his nose into other people's business, he is willing to provide emotional support and help from a distance, being more content as an observer. He has a habit of doing things alone rather than relying on others.

Kazuhiko's primary motivation is often a desire to maintain his quiet, uneventful life, but he consistently finds himself drawn into the romantic troubles of the "losing heroines" around him. He acts as a steadfast supporter and observer, helping them process their heartbreaks without being forceful. His role in the story is that of the emotional anchor for several heroines, helping them confront and recover from their failed loves, even as he remains largely oblivious to the growing romantic interest some of them develop in him.

His key relationships are central to the narrative. Anna Yanami is the first losing heroine he becomes involved with after witnessing her rejection; their relationship is built on banter and a unique dynamic where he often finds himself taking care of her. Chika Komari, a fellow literature club member, shares his hobby of tasting tap water and comes to rely on him as her rock. Lemon Yakishio is an acquaintance from middle school who also joins the literature club's orbit. His most significant relationship is with his sister, Kaju, who has an extreme brother complex and harbors feelings for him that go beyond sibling affection, though he remains oblivious. He also interacts with student council members like Yumeko Shikiya and Tiara Basori, the latter being one of the few girls he addresses by her first name.

Kazuhiko undergoes significant development throughout the series. He begins as a passive loner who is an inactive "ghost member" of the literature club. Over time, his experiences with the losing heroines force him to confront his own shortcomings and become more proactive. By taking on the role of club president, he demonstrates a new willingness to act and solve problems rather than just observing from the sidelines. He comes to accept his own egoistic tendencies and learns to act according to what he truly wants. He also gradually recognizes his desire for friendship, eventually asking Anna to formally be his friend. His physical abilities also show improvement after he begins training for an athletic competition.

Notable abilities include being an exemplary student who ranks near the top fifty in his entire grade, showing high intelligence in both academics and strategic planning. He also possesses high emotional intelligence and maturity when dealing with other people's interpersonal relationships. Kazuhiko can cook well, though he admits he is not as skilled as his sister. In contrast, he fares extremely poorly in physical activities due to a lack of regular exercise. He is also an amateur writer of romantic comedy novels, though his works have not found an audience beyond his immediate circle.