Kaori Tachibana is a high school student and a supporting character. She is in her third year and serves as the keyboardist for the band SSGIRLS. She has a tall figure, standing around 170 cm, with short hair and a distinctive fang tooth that is often visible when she smiles. A notable visual trait is that her eyes are almost always closed; on the rare occasions she opens them, her gaze can appear quite intimidating.

Her personality is laid-back and easygoing, reflected in her relaxed, dragging way of speaking. She has a cheerful and friendly spirit, often giving her close friends playful nicknames to show affection. She calls Mari Tsutsui Ma-chan, Yori Asanagi Yori-yori, and Aki Mizuguchi Aki-ki. Kaori is deeply attached to Mari, frequently hugging her or staying close by her side, and she seems happiest when she is with her. She describes herself using her own name, Tachibana-san, as a pronoun.

Within the story, Kaori is a reliable and gentle presence in the band SSGIRLS. Her calm and caring demeanor helps balance the group's dynamics, easing tensions and creating a comfortable atmosphere among the members. She is childhood friends with Mari Tsutsui, and their bond is so close that they are frequently seen together. Her everyday life involves spending time with her bandmates in the Light Music Club, where her warm personality helps to lighten the mood. While she is generally warm and gentle, she also enjoys gently teasing her friends.

Specific details regarding a significant personal arc or change in her character over the course of the narrative are not documented in the available information. Her notable abilities are centered on her role in the band, where she plays the keyboard as a member of SSGIRLS.