Kaori Tsubaki is a male Exorcist who serves as the Physical Education and practical training instructor at True Cross Academy. In terms of appearance, he is known for his very prominent sideburns, which have earned him the nickname Ol' Patillas among students. He has short brown hair, a well-defined jawline, and thick eyebrows, typically wearing the standard uniform of a teacher who is also an Exorcist. His official Exorcist qualifications include the ranks of Dragon Knight and Medical Technician Knight.

Tsubaki's personality is characterized by hyperactivity and a tendency to express his opinions quickly and openly. He is considered a problematic teacher because he consistently prioritizes his private life, particularly his romantic relationships, over his professional duties. This is most notably demonstrated by his frequent and abrupt behavior of canceling class or leaving in the middle of a lesson upon receiving a phone call from a woman he affectionately refers to as his gata, or gatinha.

His primary role in the story is as a background authority figure and supervisor for the students in the Exwire course. He is one of the teachers informed by Mephisto Pheles about Rin Okumura's demonic heritage after the boy is enrolled. During a physical education class where students are chased by Leapers, Tsubaki scolds Rin and Ryuji Suguro for treating the exercise like a race and later privately reprimands Ryuji for his behavior toward Rin, who is considered a special student. He is also present as an examiner during the promotion test for the Exwires and later, alongside Yukio Okumura, as a supervising teacher during a class mission to capture a ghost.

Information on Tsubakis motivations suggests he is primarily driven by his personal relationships, as he is known to abandon his teaching responsibilities whenever his romantic partner needs him. Key relationships include his dynamic with his students, whom he instructs and monitors, and his significant off-screen relationship with an unnamed woman he calls his gata. He also has a professional relationship with Mephisto Pheles and Yukio Okumura as a fellow faculty member. Regarding development, Tsubaki does not undergo a significant personal journey but maintains a consistent presence as an instructor. A notable feat of his is demonstrating the ability to maintain consciousness even after being possessed by Satan. As for notable abilities, while his specific Meister type and overall exorcism skills have not been fully displayed, his official titles confirm he is at least a middle-ranking Exorcist with combat and medical capabilities. Outside of school, he is also the owner of a heavy motorcycle.