Height: 157cm

She is the daughter of the president of Koshiki Real Estate. She has a gentle, airheaded nature and is somewhat eccentric—finding pitcher plants cute or being delighted to receive a haniwa (clay figurine) as a gift.

Although she fits the "rich young lady" archetype, she is completely unpretentious; yet, true to her name, she gives a traditional impression—reciting waka poetry when viewing cherry blossoms, or wearing a furisode kimono for the first shrine visit of the year and a yukata for firefly viewing. At the same time, she shows a childlike side, such as making a teru-teru bozu doll to pray for clear weather.

While aware that her family is wealthy, she understands that the assets belong to her parents; if someone remarks, "You're rich, aren't you, Koshiki-san?" she gently corrects the misconception. Consequently, despite being from a wealthy family, she never flaunts her family's fortune or tries to solve problems with money—though she does occasionally reveal a disconnect in her perspective, such as complaining that the large communal bath at the hotel during the school trip was "small."

Her defining characteristic is her laid-back nature.

She is clumsy—often falling over before she can even board a ski lift or getting a "Game Over" in shooting games without accomplishing anything—yet she is actually quite athletic, being a member of the tennis club. She also maintains a respectable level of academic achievement.

Her hobby is knitting, and she is skilled enough to finish a sweater without even taking measurements. While her leisurely pace means she isn't fast, the care she pours into her work warms both body and soul. She is also a capable cook—better than average—making her, like Nijino-san and the others, a truly domestic-minded girl. Thus, contrary to her tendency to march to the beat of her own drum to an extreme degree, she is a young lady whose capabilities are flawless, with absolutely no weak points.