Teruyo Oshie is the homeroom teacher for Hitori Bocchi's class. She has brown hair extending slightly past her shoulders, styled with a small ponytail draped over her right shoulder and secured by a silver hairpin on the right side. Her blue eyes complement her usual attire: a pink teacher's uniform and beige high heels.

Professionally composed yet visibly nervous around Sunao Nako due to Nako's delinquent appearance, Oshie displays discomfort despite Nako posing no actual threat. She prioritizes teacher-student boundaries, explicitly declining Bocchi's friendship request to maintain professional authority—an incident that distressed Bocchi.

Oshie harbors a significant misunderstanding about Bocchi, mistaking her for a "gang leader" recruiting underlings. This misconception stems from observing Bocchi's interactions with Nako and misreading Bocchi's relationship with Sotoka Luckythar, fueling Oshie's unwarranted wariness. Students use the nickname "Teru-chan," signaling approachability beneath her anxieties. Her name functions as a linguistic pun derived from "oshieteru yo" (meaning "I'll teach you"), reflecting her occupation.