Koume, a shy and sensitive child with a timid demeanor, often blushes in social situations. Her chin-length brown hair frames large, expressive brown eyes, complemented by her standard school uniform and a treasured red ribbon gifted by her older brother. This ribbon serves as a constant reminder of their bond, rarely leaving her side.

At the semester’s start, she befriends Anzu and Hiiragi, joining their activities with quiet enthusiasm. Though reserved, she reveals a playful streak when distracted by toys, especially her beloved stuffed companions—Panda Neko, Neko-san, and Usagi-san. Her whimsical dreams include owning a stuffed animal shop, flower store, bakery, or becoming a devoted wife. Favorite comfort foods like omelette rice, pudding, and meatballs reflect her youthful tastes.

While aiding Hiiragi in crafting schemes to help Anzu pursue their teacher romantically, Koume’s focus often wavers due to her easily distracted nature. Secretly, she harbors a crush on classmate Kobayakawa Yuu, hesitantly following Anzu’s bold advice to declare "Take me!"—a tactic borrowed from Anzu’s family. A group outing humorously highlights her white underwear during an energetic mishap.

Her family background mentions an older brother, though specifics remain private. Relationships with peers and teachers dominate her interactions, with no notable shifts in her circumstances or personality across documented portrayals.