Kaori Nakaseko is a third-year student at Kitauji High School, serving as trumpet section leader and band accountant, managing the group's finances. Her appearance features short, bobbed dark-brown hair, brown-reddish eyes, and a distinctive mole on her left cheek. She wears the standard third-year uniform.

Renowned for her gentle demeanor and soft voice, Kaori enjoys widespread popularity within the band, attracting devoted admirers due to her approachable nature. A skilled trumpet player herself, she objectively recognizes superior talent, demonstrated when she observes Reina Kousaka's ability during re-auditions for the "Crescent Moon Dance" solo and voluntarily declines the opportunity in Reina's favor.

Her closest band relationships are with president Haruka Ogasawara and vice president Asuka Tanaka. Interactions with Asuka often elicit moments of shyness or blushing, especially when receiving compliments. Kaori enjoys spending time with Asuka, particularly visiting cafes. Baking sweets is another hobby, consistent with her liking for sweet foods. Trained since childhood in traditional arts like tea ceremony and flower arrangement, her favorite color is white.

Beyond band activities, Kaori dislikes insects and crowded environments. After graduating Kitauji High School, she attends nursing school to pursue healthcare. Within the narrative of *Gekijō-ban Hibike! Euphonium: Todoketai Melody*, focusing on Asuka Tanaka's potential departure, Kaori maintains her established role as a supportive senior member and trumpet section leader, participating in key band events including performances and preparations for the national competition.