Yagyū attends Hanzō National Academy as a first-year student, hailed as a prodigy in shinobi arts despite her youth. Her defining trauma is the death of her younger sister Nozomi from car accident injuries shortly after Yagyū's enrollment. As a permanent reminder, she wears an eyepatch made from one of Nozomi's ribbons over her functional right eye. This loss forged her initially distant and solitary nature, leading her to rely solely on herself and shun emotional bonds. Her development sparks upon meeting Hibari, a classmate whose striking resemblance to Nozomi deeply affects Yagyū. She assumes a fiercely protective older-sister role towards Hibari, forming an intense bond that slowly opens Yagyū to others. This relationship drives her character growth, compelling her to prioritize Hibari's safety and emotional well-being above all else, rushing to her aid without hesitation. Yet, this protectiveness can cause Yagyū to underestimate Hibari's abilities or clash with others who interact with her. In the *Shinovi Versus* storyline, Yagyū's dedication faces a trial when harsh training remarks make Hibari run away on her birthday. Yagyū frantically searches, battling opponents including Katsuragi, Ryōbi, Yozakura, Minori, and Haruka, who block her path or provoke her protectiveness. Each fight strengthens her resolve to reconcile. She reunites with Hibari, gifting her every variety of Mr. Bunny candy as a peace offering. Despite ongoing tensions with rivals like Haruka, Yagyū learns to temper her aggression to honor Hibari's wish for a conflict-free celebration. The *Bon Appétit!* spin-off reveals further motivations. Yagyū enters a cooking competition with Hibari after learning the grand prize is a wish-granting scroll. Her initial plan is to use the scroll to strengthen their bond. During the tournament, she temporarily adopts an "older sister" persona towards competitors like Asuka and Daidōji. After defeating Hibari in the finals, she realizes their bond has deepened organically through the shared experience and destroys the scroll, affirming their connection needs no supernatural aid. Physically, Yagyū has long white hair styled in twin-tails with shuriken accessories, red eyes, and stands 158 cm tall. Her standard attire includes a bladed oil-paper umbrella used offensively and defensively in combat, a black mantle with triangular trim, and a red plaid skirt. Her guardian animal is a squid, mirrored in her dietary preference for eating whole dried squid without utensils. Notable traits include sporadic nosebleeds when flustered, often by discussions involving Hibari, and hay fever-induced vulnerabilities. Sensory impairment during hay fever episodes intensifies her reliance on Hibari's presence. She also harbors a fear of roller coasters, which disrupts her typically stoic composure. Her combat style emphasizes precision and evasion, leveraging expertise in concealing her presence and manipulating her umbrella to generate whirlwinds or block attacks. This proficiency, combined with tactical adaptability, allows her to defeat higher-ranked opponents despite her novice status.