Kazuha Toyama, a spirited high school student from Osaka, shares a lifelong bond with Heiji Hattori, their friendship rooted in their fathers’ roles as Osaka police colleagues. In *Magic File 4: The Osaka Okonomiyaki Odyssey*, she races alongside Conan Edogawa and Heiji to savor okonomiyaki before Conan’s departure, only to intercept a distressed woman entrusting them with an infant named Kaoru. Kazuha’s sharp observation reveals the child’s disguised gender, unraveling a kidnapping plot. The woman later returns, clarifying her husband’s mistaken paternity belief from a *Tale of Genji* allusion. Though the case closes, Kazuha’s culinary hopes dissolve with sudden schedule shifts. Her bond with Heiji originated in childhood when they were handcuffed for days without a key, an ordeal inspiring Kazuha to forge matching talismans from the cuffs’ chains. She later embedded Heiji’s photo into her charm, silently symbolizing her affection. Their dynamic thrives on bickering and mutual denial of romance, though Kazuha openly admits her feelings to others. Jealousy flares when Heiji references "Kudo," initially misdirecting her suspicion toward Ran Mouri until Shinichi Kudo’s identity surfaces. Hot-tempered yet fiercely loyal, Kazuha wields a 2nd-degree aikido black belt to disarm threats and shield allies. Her deductive prowess occasionally outpaces seasoned detectives, though she defaults to supernatural theories for mysteries, contrasting her pragmatic crisis responses. She bonds with Ran over martial arts and the complexities of loving detectives entangled in danger. Pivotal moments test her resolve: clinging to a cliff’s edge, she stabs Heiji’s hand to save him, only for his refusal to release her to defy fate. Later, kidnapped by a lawyer coercing Heiji to crack a code, his tactical near-confession—a ruse—leaves their tension unspoken. Kazuha’s own confessions falter against Heiji’s obliviousness, echoing Ran and Shinichi’s unresolved ties. Daughter of Osaka police official Ginshiro Toyama, Kazuha’s interests span competitive karuta and kaiju films, reflecting her playful tenacity. Her design features a vibrant ponytail secured with ribbons mirroring her outfits, paired with a versatile wardrobe blending casual ease with occasional elegance.