Shigure Kōsaka is the youngest and only female master at Ryōzanpaku dojo, serving as the weapons master. She possesses distinctive lightning bolt-shaped eyebrows, fair skin, and long black hair usually tied in a high ponytail. Standing 159 centimeters tall, she has a slender, curvaceous figure. Her typical attire includes a short pink kimono, purple stockings, a fundoshi underneath, and bandages wrapped around her chest. For serious combat, she wears chainmail secured by a black chest strap. She always carries her late father's nodachi strapped to her back, its hilt wrapped in bandages due to the missing tsuba.

Raised nameless in mountain isolation by her father, the weaponsmith and practitioner Hachirobe, her life shifted when martial artist Akisame Kōetsuji discovered them. Terminally ill, Hachirobe deliberately provoked Akisame into a duel, seeking a warrior's death while intending it as a cautionary lesson against his own violent path. After witnessing her father's fatal fall from a cliff, the young Shigure clung to his final forged sword as her sole memento. Akisame named her "Shigure" (drizzle) inspired by the rainy conditions during their meeting and entrusted her to his elderly friend, the master of Kōsaka-style weapons combat. Following this mentor's death, Akisame brought Shigure to Ryōzanpaku.

Initially a detached loner, Shigure avoided social interactions with fellow residents, save for sporadic exchanges with Apachai Hopachai. Her core philosophy asserts weapons are extensions of the body, not mere tools, and mastery requires transcending reliance on a weapon's inherent power. She consistently applies Katsujinken (life-saving fist), disarming opponents non-lethally, often by slicing their clothing—a tactic particularly effective against female adversaries who typically cease fighting to cover themselves. Despite her reserved exterior, she shows fierce loyalty to Akisame, viewing him as a surrogate father and complying with his requests without hesitation. She reacts violently to Kensei Ma's inappropriate behavior yet retains feminine sensitivities, blushing when acknowledged as a woman during Akira Hongō's refusal to duel her.

Kenichi Shirahama's arrival spurred significant character development. Shigure gradually integrated into communal activities like shared meals and displayed subtle emotional shifts, including rare smiles during Kenichi's combat achievements. Though she trains Kenichi less frequently than other masters, she exhibits persistent disappointment regarding his reluctance toward weaponry and covertly yearns for more instructional opportunities. Their relationship features unusual intimacy, as she bathes nude alongside him without discomfort and suggests repeated joint bathing. A recurring comedic element involves her lack of modesty, appearing scantily clad when awakened, fighting opponents naked, or fishing nude—actions that frequently unsettle observers. Paradoxically, she displayed embarrassment when captured nude by Yami researchers after they confiscated her weapons.

Her capabilities establish her as an exceptional martial artist. Bearing the title "Prodigy of Sword and Mistress of all Weaponry," she demonstrates proficiency with virtually any armament—swords, projectiles, chains, tonfas—even transforming mundane objects like wooden spoons into lethal instruments. She conceals numerous weapons beneath her clothing and achieves the pinnacle of swordsmanship: fusion with her blade. Notable feats include single-handedly engaging Yami's seven-member Hachiō Danzaiba to facilitate Kenichi and Miu's escape, though divided focus contributed to her eventual capture. She possesses extraordinary speed enabling instantaneous multi-strike flurries that overwhelm electronic sensors in sword-fighting games, necessitating deliberate slowdowns. Her agility permits seamless rooftop traversal and wall-scaling mobility, while her strength allows cleaving metal objects like tank cannons with blunt implements followed by manual insertion into the tank's hull. She excels in stealth infiltration, often materializing silently or employing camouflage. Additionally, she inherited her father's blacksmithing expertise, capable of forging protective gear using traditional ferrous metallurgy techniques and crafting weapons from raw materials like iron sand derived from river sediments.

Distinctive traits include sleepwalking accompanied by unsettling mutterings that disturb Sakaki, profound affection for animals—particularly her pet mouse Tōchūmaru whom she fiercely protects—and rapid skill acquisition in non-combat domains like theatrical roleplay, convincingly impersonating Miu's mother despite Sakaki's struggles. Shigure undertakes confidential missions to retrieve swords forged by her father, removing them from circulation and preventing their misuse for killing, honoring her father's legacy. Her confrontation with Yami's Executioner Blade underscores this commitment.