Mishio Usa is a student at Otogi All-Girls High School. She wears her hair in a bun with two front locks framing her face and typically sports oval-shaped glasses with her school uniform.

Her personality is extroverted and energetic, sometimes excessively so. She engages directly, like slamming Nasa's back during programming class to demand his contact information, and freely discusses personal topics such as name origins and romantic advice.

During Nasa's programming class at her school, she actively participates and asks about his name and background. She later visits his home for supplementary lessons with classmates, though the session turns into a sauna endurance contest she wins as heat endurance champion.

Mishio offers romantic guidance to Nasa, suggesting outwardly calm individuals like Kaguya Gekkō can hide intense jealousy with unpredictable reactions. Mishio herself harbors personal feelings for Kaguya.

For her film research club, she serves as cameraperson on a low-budget horror project. She notes a member's absence during filming but continues working while others search, maintaining a strictly observational role with minimal on-screen presence.

She participates in school clubs and group events but remains on the periphery of central narratives. Her background, family history, and future developments are not documented in available materials.