Tamaki Kousaka is a childhood friend of Takaaki Kouno, alongside Konomi Yuzuhara. She returned after years at a boarding school to attend the same high school as Takaaki, fulfilling a promise made before her departure. Physically tall, she possesses butt-length red hair typically tied in a ponytail and orche-brown eyes.

Her personality is strongly dominant and protective, often acting as an elder sister figure to both Takaaki and Konomi. She exhibits natural leadership and frequently mediates group dynamics. Despite her confident exterior, moments of vulnerability surface, such as embarrassment when pressured about her relationship with Takaaki.

Within Takaaki's social circle, Tamaki acts as a stabilizing force. She organizes gatherings, like inviting female characters for tea to thank them for supporting Takaaki, demonstrating her awareness of their connections to him. Romantic tension exists between Tamaki and Takaaki, complicated by her close bond with Konomi, who also harbors feelings for him. In the "Another Days" storyline, Tamaki's internal conflict leads her to contemplate sharing a future with both Takaaki and Konomi to preserve their familial bonds.

In the fantasy spin-off "Dungeon Travelers," Tamaki adapts as a fighter-class character, utilizing martial prowess in combat. This adaptation retains her protective instincts within a genre-shifted context separate from her core development.

Various OVAs document Tamaki's reactions to situational comedies, such as her flustered response to being questioned why Takaaki doesn't use her first name without honorifics, adding nuance to her typically composed demeanor. Her return from boarding school triggers renewed connections and unresolved emotions with Takaaki, driving narrative elements centered on childhood promises and evolving relationships.

Her role remains consistent throughout as a protective figure navigating complex emotional ties within the group dynamic.