Kyouya Nagi, paternal cousin of Itsuomi Nagi, manages a small bar. In his early twenties, he possesses short cropped dark hair, a sweet face, and an easygoing presence, complemented by a calm and friendly demeanor that endears him to patrons. His past includes a six-year romantic relationship that dissolved despite his efforts, making him guarded about expressing his own emotions in new relationships. This contrasts with his willingness to offer romantic advice to others and his avid interest in celebrity romance rumors and interpersonal dynamics.

He befriends Yuki Itose after meeting her through Itsuomi, showing curiosity about her bond with his cousin. To communicate effectively with her, he learns sign language. Simultaneously, he develops feelings for Rin Fujishiro, Yuki's best friend and a bar regular. Though mutual interest exists, Kyouya hesitates to act due to his reserved nature and past heartbreak.

Their relationship progresses gradually. A turning point occurs when Rin loses her apartment key and stays overnight at his place, fostering closeness. Later, during a sign language training camp, Kyouya gains confidence and initiates a formal relationship with Rin, overcoming his reluctance.

His name carries layered meanings: "Kyou" translates to "capital city," and "ya" means "increasingly" or "all the more," while his surname "Nagi" combines "wave" or "breaker" with "giving." He has blood type B and is occasionally called "Kyou" by close friends.