Kenta Yamazaki is a male student at Fujishi High School, where the story is set. Initially, he is known as a shut-in who has completely withdrawn from school life and isolated himself in his home. This reclusive behavior is the result of a specific and painful romantic rejection. Kenta had been pursuing a girl he liked, but she manipulated his feelings to get closer to the leader of a club, and after she succeeded, she and her new boyfriend cruelly mocked him for his efforts. This experience left him deeply hurt, fueling a prejudice against popular, sociable people, whom he sees as superficial and untrustworthy.

At the start of the narrative, Kenta holds a strong grudge against the school's elite, and he particularly resents Saku Chitose. He labels Saku a flippant playboy or a jerk, viewing him as the embodiment of everything he dislikes about the popular crowd and the unfairness of high school social hierarchies. However, his motivation for eventually leaving his isolation is a desire for revenge against the girl who rejected him. He decides to participate in a time-limited plan, guided by Saku, to transform himself and prove his former crush wrong.

As a character, Kenta is introduced as quiet, reserved, and awkward in social settings. He is not used to the vibrant and energetic atmosphere of Saku’s friend group, which he finds overwhelming at first. Despite his initial hostility and defensive demeanor, he possesses an underlying openness to change and a willingness to improve himself. His core personality traits include a sense of sincerity; once he begins to engage with others, he comes to value honest communication and gradually learns to express his true feelings.

Kenta’s primary role in the story is as a catalyst and a student figure. His struggle to return to society and his subsequent transformation form a major early narrative arc. Saku’s task, assigned by a teacher, is to convince Kenta to come back to school, and this mission drives a significant portion of the initial plot. Through his journey from isolation to community, Kenta’s evolving confidence and authenticity inspire those around him and add emotional depth to the series' coming-of-age themes.

His most significant relationship is with Saku Chitose, who acts as a mentor figure. Despite their confrontational first meetings, Saku persistently and genuinely attempts to connect with Kenta, guiding him on social skills, lifestyle changes, and helping him reintegrate into school life. Kenta also forms bonds with other members of Team Chitose, including his male peers Kaito Asano and Kazuki Mizushino, becoming a trusted member of their circle over time. He faces antagonism from another popular student, Atomu Uemura, who disapproves of Kenta’s sudden rise in social status and association with Saku, leading to conflict between the two groups.

Kenta’s development is marked by a noticeable glow-up and a significant boost in self-confidence. He undergoes a makeover, learns to navigate social situations, and practices interacting with others. While his progress is rapid, it is not without setbacks; he remains sensitive to criticism and can be easily swayed by the harsh words of others, which sometimes undermines his newfound confidence. Nevertheless, he gradually grows from a bitter, self-isolated individual into an emotionally stronger and more authentic person capable of standing on his own. In terms of abilities, Kenta does not possess any extraordinary skills. His notable achievements are entirely social, such as learning to manage his appearance, hold conversations, and attempt to re-enter his old social circles with a new sense of self-respect.