Yosshii, commonly called Yoshi, is a high school student belonging to Nagatoro, Gamo, and Sakura's social circle. Her simple-minded, childlike personality manifests through frequent mimicry of others, particularly Gamo, with repetitive speech patterns cementing her role as the comedic "boke" in group dynamics. She sports dark blonde twin braids accented by a signature curly lock atop her head, hazel eyes, and pale skin. Over time, her design reflects puberty-related changes in height and bust size, while her iconic curl humorously grows larger in later manga chapters.

Energetic and playful, Yosshii joins her friends in teasing Senpai, though her antics lack malice and stem more from peer influence than personal intent. Her occasional absent-mindedness leads to struggles with basic tasks and navigation in crowded spaces. Born November 23, she ranks as the group’s second youngest and harbors childlike hobbies like collecting plush toys and caring for her miniature dachshund. She openly admires Senpai’s manga talent, dubbing him "Sense" as a shorthand for "Manga no Sensei," and enthusiastically follows the fictional pop trio YabaT.

While her repetitive dialogue often masks deeper emotions, Yosshii subtly aids Nagatoro’s romantic endeavors through these surface-level interactions. Her unwavering loyalty to the group and consistent support of Nagatoro’s relationship with Senpai remain central traits, despite limited character development across official media. No supplemental material expands on her involvement in spin-offs or alternate storylines.