Kentarô Tsubaki is a secondary character in the narrative, introduced as a second-year student at Suzaku High School who becomes a member of the Supernatural Studies Club. He is a returnee student, someone who has spent time living abroad, which initially contributes to a feeling of being out of place among his peers. Physically, Tsubaki is notably shorter than most of the other male characters, with messy green hair and light green eyes. He is almost always seen with a toothpick in his mouth, an enduring part of his design that adds to his somewhat laid-back and casual image.

At first, Tsubaki comes across as a loner who prefers to keep to himself, spending his free time at the game center or cooking alone. This solitary nature is partly a result of his status as a returnee, which makes him feel disconnected from the established social circles of the school. Despite this initial distance, he is revealed to have a significant, though initially superficial, crush on Urara Shiraishi, the top student and one of the main characters. His feelings for her are based more on admiration from afar than on a deep understanding of her personality. However, Tsubaki's role in the story truly begins when his emotional state is revealed to have dangerous consequences. He has a peculiar habit of coping with sadness or disappointment by cooking tempura in an old school building. This habit spirals into a major crisis when a vision of the future, seen by the witch Maria Sarushima, shows that his actions will lead to a fire that threatens to burn down the school.

This incident serves as the catalyst for his integration into the main group. The protagonist, Ryû Yamada, works to prevent this future by trying to stop Tsubaki from confessing his feelings to Shiraishi and experiencing the rejection that triggers his destructive cooking spree. After the crisis is averted, Tsubaki learns about the existence of the witches and their powers, primarily through the body-swapping ability that Yamada possesses. Following this, he officially joins the Supernatural Studies Club. His personality begins to shift noticeably as he becomes part of the group. He forms a tight bond with fellow club member Miyabi Itô, and despite his initial rivalry with Yamada, he develops a deep respect for him as a friend. Tsubaki is characterized by his honesty, often saying exactly what is on his mind without a filter. As he grows closer to the group, he cheerfully gives up his hopeless crush on Shiraishi and settles into a genuine friendship with her.

Within the club, Tsubaki is a loyal and reliable member, though his straightforward and sometimes simple-minded nature provides comedic relief. He participates in several major story arcs, including the conflict to regain lost memories and the election campaign against the student council. He is willing to help his friends in unconventional ways, such as agreeing to switch bodies with Yamada to help infiltrate an opposing faction. His development is subtle but positive, transforming him from a lonely outsider into a cheerful and integral part of the club.

Tsubaki possesses a few notable abilities that set him apart. Despite his small stature, he is exceptionally strong and is considered the most formidable fighter among the male characters, easily able to overpower both Yamada and Toranosuke Miyamura at the same time. His primary talent, however, is his expert cooking skill, specifically his ability to prepare tempura and other Japanese dishes. This skill is a recurring character trait and is often shown in scenes where he is cooking for his friends in the clubroom. He is also a very skilled video game player, easily defeating Yamada at a variety of games. His fighting strength, combined with his simple honesty and unexpected culinary expertise, makes him a unique and valuable member of the group, even if he is not a central figure in the search for witches. In the long term, Tsubaki pursues his passion professionally, as he eventually becomes a chef after graduating from high school.