Yuna Wakao is a teenage girl distinguished by brown hair, typically worn in long twin tails, and ochre or amber eyes. She stands 157 cm tall with bust-waist-hips measurements of 82-53-83 cm. Her common attire includes school uniforms, pinafore dresses, and accessories like a pet collar and bow tie.

Her background originates in profound loneliness stemming from her mother Megumi Wakao's demanding work schedule, leaving Yuna frequently isolated. This isolation ceased when Megumi married Kazuma Wakao, granting Yuna both a stepfather and a stepbrother, Kyousuke Wakao, fulfilling her desire for a complete family. Following Kazuma's death from heart disease, the family structure shattered. Kyousuke, harboring resentment towards Megumi, demanded she and Yuna leave. To prevent this expulsion, Megumi proposed a deal granting Kyousuke unrestricted authority over Yuna, explicitly excluding only her virginity. Yuna consented to this arrangement to maintain her family unit.

Her core motivation is a deep-seated dread of returning to isolation, compelling her compliance with Kyousuke's demands. This includes engaging in activities aligned with his sadistic preferences. Sustained compliance triggers a psychological shift, cultivating masochistic tendencies that intensify her interactions with Kyousuke. Their relationship evolves into a complex dynamic where her submission fuels his dominance, fundamentally reshaping her behavior and emotional landscape.

Yuna appears as a main character in the visual novels "Gimai ~Haitoku no Chigiri~" and "Gibomai ~Haitoku no Kyouen~", and holds a secondary role in "Gibo Shimai". Her narrative consistently focuses on familial preservation, psychological adaptation to trauma, and the erosion of personal boundaries under coercive pressure.