Kaji Tetsuji is a student at Hideo Middle School, attending the same grade as his classmates Ayu Tateishi and Nina Sakura. He holds a prominent social position on campus, widely recognized as the school idol due to his cool, good-looking appearance. With brown hair and brown eyes, his look is typically completed by a standard school uniform. He is also a member of the school's baseball club, where he serves as the team's ace player. His best friend is Hiroki Tsujiai, who is the captain of the boys' tennis club.

On the surface, Kaji presents himself as a friendly and approachable person, always offering a pleasant smile to everyone he meets. This charm has earned him a large following of admirers who constantly shower him with gifts, including students from the third grade. However, this outgoing and nice persona is revealed to be a carefully maintained facade. In truth, Kaji is an introverted individual at heart who genuinely dislikes receiving presents from strangers and prefers to keep his real feelings and private thoughts closely guarded.

The primary motivation behind maintaining his "nice person" image is his romantic affection for Ayu Tateishi. He works hard to uphold this persona because Ayu once told him that she liked that kind of person. His role in the story is closely tied to this secret, as he becomes closer to Nina Sakura after she is the one to discover the true nature hidden behind his popular facade. His documented storyline culminates in him eventually beginning a romantic relationship with Ayu Tateishi. As a student and baseball club member, his notable abilities lie in his athletic skill as the team's ace, though he does not possess any magical capabilities.