Tamaki Nekoyama, Suzu Nekoyama's older sister, shares a home with her and exhibits a distinctly catlike personality. She frequently stays at others' houses, naps on laps, and enjoys teasing people, particularly her younger sister Suzu, with a devilish playfulness.

Initially depicted as dating multiple women simultaneously and suffering constant hangovers, she is regularly encountered by Suzu with different partners. Acquaintances label her "extremely lewd" and "not as pure as her sister," noting her promiscuous tendencies. This behavior causes discomfort for some who rely on her to listen to their complaints despite struggling with her presence.

Her heavy drinking results in memory loss when intoxicated, leading to complete uninhibition. However, her romantic focus undergoes a substantial transition as she shifts entirely toward devotion to Sawako Hebizuka. This relationship marks significant development, culminating in her inviting Sawako home for the first time – a departure from her previously scattered romantic engagements.

As a university student and senior to characters like Torao and Ryuuzaki, she demonstrates awareness of their relationships. Tamaki also fulfills family responsibilities, occasionally sending Suzu on errands that trigger encounters with other characters. Her character design reinforces the series' animal motif through her feline behavioral traits and mannerisms.