Yuki Kusakabe is a Yuki-onna, a Snow Woman, living in a modern world where demi-humans coexist with humans. She possesses fair white skin, turquoise hair, and distinctive yellow eyes. Her body temperature remains consistently colder than a human's average. Physiologically, she has minimal sweat glands and is highly susceptible to overheating, which can cause her to faint in warm environments. Negative emotions trigger physical manifestations: her tears freeze, cold air visibly emits from her feet, and a localized cooling effect surrounds her immediate vicinity.

Initially, Yuki was intensely shy and socially withdrawn, stemming from fears rooted in Yuki-onna folklore. She believed her presence could unintentionally freeze and harm others. This anxiety caused her to avoid physical contact and social interactions, particularly with classmates like Hikari Takanashi and Kyoko Machi. Her misunderstood abilities led to brief bullying, with peers perceiving her as arrogant or aloof.

A pivotal change occurred when biology teacher Tetsuo Takahashi scientifically assessed her capabilities. He demonstrated her cold aura posed no danger and her freezing was limited to her own tears and sweat. This revelation alleviated her fears, enabling her to embrace friendships. She formed a close bond with Hikari, whose vampire nature drew her to Yuki's cooling effect; Hikari frequently hugs Yuki and nibbles her shoulder to relieve fang discomfort. Yuki also developed a trusting relationship with Takahashi, regularly visiting his office for guidance and accepting his comforting hugs. Her friendship with Machi flourished once her self-imposed isolation ended.

Yuki harbors a deep passion for manga across multiple genres, an interest that embarrasses her. Her personality includes a quiet appreciation for crude humor and silliness, contrasting her typically reserved demeanor. Over time, she became significantly more expressive and cheerful. This personal growth is symbolized by a change in the series' opening titles, where her segment transitions from a winter backdrop with a somber expression to a spring setting showing her offering a joyful wave.

Her background story focuses exclusively on her high school experiences and journey of self-acceptance and social integration.