Koushi Usa is a physical education teacher at Aoba High School, where he also serves as the homeroom instructor for class 3-4 and the advisor for the boys’ volleyball club. He is twenty-seven years old, stands one hundred seventy-eight centimeters tall, and has short brown hair with a small side bang and brown eyes. His typical attire consists of an orange shirt and knee-length shorts, often accompanied by a sports whistle.

Outwardly he presents a calm appearance, but his personality is fiery and impulsive, quick to bark with the intensity of a wild animal when provoked. He shares a combative yet friendly rivalry with fellow teacher Kokoro Amatsu, with whom he graduated from the same university. The two constantly bicker and compete, particularly over the performance of their respective sports clubs, and Koushi often tries to tease her. Because the boys’ volleyball team lacks strong results, he is frequently on the receiving end of Kokoro’s taunts. Despite the bickering, their relationship is underpinned by a long-standing mutual respect and a shared dedication to their students.

As a supporting figure in the school, Koushi contributes to the everyday life of the students, overseeing physical education classes and striving to motivate the members of his volleyball club. His competitive streak and hot-blooded coaching style reflect a deep-seated desire to see his team improve, even if their current level leaves him open to good-natured ridicule from his colleague. In the school environment, his presence adds a layer of spirited energy and helps illustrate the varied dynamics among the adult staff who shape the student experience.