Yuuna is a young girl with short red hair that usually has a flower pin on the left side with a buttoned sweater and skirt.
Okuyama is very mature for her age. In contrast with Souta Hori's carefree and trusting nature, she is much more cynical and cautious. She often scolds Souta and their classmates for their childish behavior, but mostly because she is self-conscious of her forehead, which she thinks is too large. However this feeling about herself changed after Izumi Miyamura told her that she looked pretty.
Okuyama and Souta are friends and classmates. When asked by Syu Iura if they are "just friends", she says "obviously", noting that it's still 10 years too early for Souta to understand. Okuyama often goes over to the Hori household after school to play with Souta.
Okuyama looks up to Hori as an older sister. She thinks of her as kind, cute and good at cooking. In addition, the two share a similar aesthetic when it comes to Hori's handmade stuffed animals.
- The name Yuuna means "exist" (有) (yuu) and "vegetables, greens" (菜) (na).
- Yuuna's surname Okuyama means "back, inner part" (奥) (oku) and "mountain, hill" (山) (yama), which literally means "remote mountain, mountain recesses" altogether.