Kaori Sekiya is an associate of Keiya Utou, connected through his work with the Senagaki yakuza clan. Her background is within that world, as she previously worked as a hostess at a traditional club managed by the Senagaki clan. In this role, she is identified as a colleague of Keiya and someone who understands the environment he comes from.

Kaori has a personal history with Keiya that predates the main events of the story. The two were involved in a physical relationship, specifically a one-night encounter that occurred when Keiya first joined the Senagaki clan. Despite this past intimacy, Kaori makes it clear that she is not, and has never been, Keiyas girlfriend. She demonstrates a level of honesty and directness about this history, as she openly confirms the nature of her past with him when asked directly.

In her limited appearances, Kaori serves as a figure who helps the protagonist, Isaku Senagaki, gain clarity about her own feelings. During a school festival, Kaori visits the school, greeting Isaku with a hug and explaining that she simply wanted to see how Keiya was doing while at school. Her presence triggers Isakus recollection of seeing her kiss Keiya in an earlier episode, which forces Isaku to confront her own jealousy and question the true nature of Keiyas relationship with other women. Later, Isaku proactively seeks her out, and Kaori directly answers her questions about her past with Keiya, providing Isaku with the confirmation she needs to understand Keiyas past and her own desire for a future with him. Her role in the story is therefore functional, acting as a catalyst for the development of the central romance.