Freesia Yagyu is the biological daughter of the historical swordsman Yagyu Jubei Mitsuyoshi and his Siberian wife, Trusia. Her origins lie in 17th-century Siberia, where Jubei was sent to assassinate Kita Ressai, leader of the Northern Yagyu clan. During this mission, Jubei fell in love with Trusia and fathered Freesia. Though Jubei sought to protect her from swordsmanship, Freesia displayed innate talent, mimicking his techniques with twigs from a young age. A pivotal duel between Jubei and Kita Ressai on a frozen river caused catastrophic ice collapse. Trusia drowned attempting to save Freesia, who then plunged into freezing waters and remained encased in glacial ice for roughly 300 years. Thawed in the modern era by global warming, she emerged physically unchanged in Hokkaido.

Following her awakening, Freesia survived the wilderness with animals who sheltered and raised her, fostering a lifelong ability to communicate with wildlife. Learning of her parents' deaths and the existence of the "Lovely Eyepatch"—an artifact containing her father's techniques bequeathed to Jiyu Nanohana—Freesia crafted a makeshift "Spade Eyepatch" to channel her ancestral swordsmanship. Believing herself the rightful heir to Jubei's legacy, she traveled to Japan, enrolled as a transfer student at Jiyu's school, and initiated a calculated campaign to reclaim the Lovely Eyepatch.

Freesia exhibits a marked duality. Publicly, she adopts a cheerful, hyperactive demeanor to integrate into society and befriend Jiyu, masking her vengeful objectives. Privately, she harbors intense resentment towards Jiyu, viewing her as an usurper. Her envy fuels manipulative tactics: she ingratiates herself with Jiyu's father, Sai, and engineers scenarios to isolate Jiyu socially, including falsely claiming Jiyu rejected Sai's paternal role, triggering a violent confrontation. Her combat style mirrors her emotional volatility; her Spade Eyepatch-amplified swordsmanship is ferocious and bloodthirsty, contrasting with Jubei's technical precision. Though repeatedly battling Jiyu with intent to inflict suffering, she explicitly avoids lethal force, seeking to emotionally cripple her rival.

Her character arc pivots on internal conflict between vengeance and burgeoning empathy. Prolonged proximity to Jiyu and Sai fosters genuine affection, complicating her mission. After temporarily defeating Jiyu and seizing the Lovely Eyepatch, she experiences profound dissatisfaction, realizing victory fails to alleviate her anguish. This catalyzes a psychological breakdown, culminating in a spiritual encounter with her father's ghost. Jubei reveals his true wish—for Freesia to live unburdened by the sword—and clarifies that both her Spade Eyepatch and Jiyu's Lovely Eyepatch embody legitimate aspects of his legacy. This revelation shatters Freesia's vendetta, prompting tearful reconciliation with Jiyu.

In the series finale, Freesia collaborates with Jiyu to confront Kita Ressai's vengeful spirit, manifested as an ice giant. Their synchronized swordsmanship and mutual trust enable a fusion technique that summons Yagyu Jubei's spirit to defeat Ressai. Freesia's redemption concludes with Jubei entrusting her to Sai's guardianship. Epilogue sequences depict her transitioning to a peaceful life as an ordinary student, her hostility fully resolved.

Freesia's abilities include masterful swordsmanship derived from her lineage, enhanced physical strength evident since childhood, multilingual fluency in Russian and Japanese, and her unique, persistent connection to animals reflecting her formative years in the wild.