Yukie Mayuzumi arrives at Kawakami Academy as a first-year transfer student. Eldest daughter of Sword Saint Taisei Mayuzumi, she was raised in Ishikawa Prefecture under a strict martial arts tradition. Yukie trained rigorously from childhood in the Mayuzumi swordsmanship style to succeed her father, while her mother taught traditional etiquette. This upbringing hindered her social development, resulting in awkward interactions, unintentionally intimidating smiles, and difficulty forming friendships. Her isolation led her to create Matsukaze, a horse-shaped phone strap she uses as a ventriloquist proxy to voice her inner thoughts and emotions.

Physically, Yukie is notably tall with pale skin. She has deep forest-green hair styled in long pigtails tied with white ribbons and dark blue eyes. Her appearance is often described as embodying the "yamato nadeshiko" ideal of grace and traditional femininity, with emphasis on her voluptuous figure.

Her personality combines extreme shyness, humility, and non-assertiveness. She frequently apologizes, assumes blame for awkwardness, and consults Matsukaze to navigate interactions. Privately, she harbors a perverse side, researching erotic material and exhibiting masochistic tendencies in romance. She refuses to part with her katana, viewing it as the "house of her soul," though she gradually learns to leave it aside in social settings after joining the Kazama Family.

Yukie wields her katana with exceptional proficiency. She earned the title of one of the Four Devas by defeating Takae Tachibana, though this remains largely unknown. Considered the weakest among the Four Devas, she nonetheless demonstrates formidable combat ability, holding her own against elite fighters like Gyoubu Shakadou and Yoshitsune Minamoto. Her fighting style undergoes a dramatic shift: shedding timidity in battle, she exhibits fierce confidence and discipline. Yukie avoids conflict but becomes ferociously protective when friends or loved ones are threatened, unleashing an "Asura-like" aura in moments of intense rage.

Her development centers on integration into the Kazama Family. Initial attempts to befriend the group involved offering food and candies, often ending in flustered retreats. She formally requested to join, becoming the ninth member after fainting from anxiety during Shouichi Kazama's teasing acceptance. Nicknamed "Mayucchi" or "Mayumayu," she gradually grows more outspoken, calm, and happy within the family. Her reliance on Matsukaze diminishes over time, though she retains the ability to imitate its voice. Her natural smile emerges more frequently, making her less intimidating.

Yukie forms meaningful bonds, particularly with Yamato Naoe. She initially feels a platonic affinity for Gakuto Shimazu, who reminds her of her father, but develops romantic feelings for Yamato. These feelings deepen, leading to scenarios where she engages in sexual activity with him or masturbates while imagining him. Her route in "Majikoi! S" depicts growth: she becomes more cheerful and outgoing, openly expresses affection, and gains popularity. Her protective instincts intensify when loved ones like her sister Sayaka or Yamato face danger.

Her background includes a complex family dynamic. She admires yet envies her younger sister Sayaka for her social ease, contrasting with her own struggles. Her father, remembered as "tough but kind," and her mother are deeply respected. Alternate timelines in "Majikoi! S" explore scenarios where earlier connections with the Kazama Family alter her social trajectory, though her core traits remain consistent.

Yukie represents the martial virtue of Respect (礼, Rei). Her evolution from a socially isolated swordsmaster to a more integrated, self-assured individual underscores her narrative, balancing lethal combat skills with her enduring quest for human connection.