Mizore Shirayuki is a Yuki-Onna, a snow woman from Japanese folklore, who attends Yokai Academy, a school for monsters. She initially appears as a new transfer student late in the school year and quickly becomes a member of the Newspaper Club. Her background is marked by a painful incident in which she developed a crush on a teacher named Okuto Kotsubo, only to have him take advantage of her feelings. When she realized his true intentions, she froze him in self-defense. This event led to widespread rumors and social ostracism, making her deeply distrustful of others and leaving her feeling isolated and depressed.

Mizore's personality is initially quiet, stoic, and withdrawn, reflecting her loneliness and emotional vulnerability. She is a deeply sensitive individual who craves connection but fears rejection. Her primary motivation is her intense romantic attachment to Tsukune Aono, the human protagonist attending the monster school. She sees in him a kindred spirit, someone who appears as lonely as she feels, and she becomes utterly devoted to him. This devotion manifests as obsessive stalking behavior, which becomes a recurring comedic element in the series. She keeps a scrapbook of his newspaper articles, follows him constantly, and appears suddenly in unexpected places such as under desks, in lockers, or from the ceiling. Despite this obsessive exterior, she is capable of genuine tenderness and loyalty, and over time she learns to trust and open up to others.

Within the story, Mizore serves as a supporting protagonist and a key member of Tsukune's inner circle. Her role involves both comedic relief through her possessive antics and serious contributions during conflicts, where her ice powers make her a formidable fighter. Her character arc focuses on overcoming her traumatic past and learning to form meaningful connections beyond her obsession with Tsukune.

In terms of relationships, her bond with Tsukune is the emotional anchor of her character. She loves him deeply and resolves to stay by his side even if he never returns her feelings. She has a competitive and often combative rivalry with Kurumu Kurono, another of Tsukune's admirers, but this rivalry eventually deepens into a close and loyal friendship, with the two training together and fighting side by side. She respects Moka Akashiya as both a rival for Tsukune's affection and a trusted friend. She also shares a good relationship with Yukari Sendo and looks up to Ginei Morioka as a mentor figure who helps her improve her combat skills.

Mizore undergoes noticeable development throughout the series. She begins as a socially isolated stalker but gradually becomes a more confident and integrated member of the group. After Tsukune intervenes to protect her from the teacher who once betrayed her, she regains her ability to trust. Later, she decides that even if Tsukune does not love her back, she will follow and protect him forever. In the manga, she trains rigorously with Kurumu to master her abilities and fights alongside her mother, Tsurara Shirayuki, in major battles, ultimately emerging as a self-possessed and proud warrior.

Mizore's primary abilities stem from her Yuki-Onna nature. She has cryokinetic powers, allowing her to manipulate ice and snow at will. She can freeze objects and her surroundings, form ice claws around her hands for combat, and create sharp ice projectiles such as daggers or icicles. She can also produce ice clones of herself or others, which are fragile but capable of independent thought. With training, she learns to freeze and control entire bodies of water in her vicinity. When she uses her full power, her hair transforms into ice. A notable weakness is her vulnerability to heat and fire, which is why she constantly sucks on a lollipop to regulate her body temperature and prevent overheating.