Kotarou Inugami is a half-demon (hanyō) distinguished by canine traits: pointed ears, a white-tipped tail, and sharp fangs. His spiky brown hair is often tied in a ponytail with framing bangs, and he favors casual attire like a brown jacket, cream shirt, pants, and sneakers. Born an outcast from both human and dog-yōkai societies, Kotarou endured a lonely childhood. This isolation ceased when he formed connections, notably with former adversary Negi Springfield. During the Kyoto arc, he served as a mercenary under Chigusa Amagasaki, tasked with hindering Negi and Asuna Kagurazaka. He trapped them in a dimensional loop but was defeated by Negi, aided unintentionally by Nodoka Miyazaki. A rematch was interrupted by Kaede Nagase, who discerned Kotarou was holding back. The Kansai Magic Association subsequently imprisoned him, sealing his transformative and spirit-summoning powers. Refusing an assassination offer from Fate Averruncus, he escaped to Mahora Academy to challenge Negi again, viewing him as his sole equal rival. After intercepting Graf Hermann and the Slime Sisters and stealing a critical item, he suffered amnesia from a confusion spell during his escape. Discovered by Chizuru Naba and Natsumi Murakami, who mistook him for a stray dog, they nursed him back to health. He later aided Negi in rescuing Chizuru from Graf Hermann, earning a pardon and the restoration of his powers. Kotarou then transferred to Mahora Academy's elementary division, adopting the alias Kotarou Murakami as Natsumi's purported younger brother. He resided with Chizuru, Natsumi, and Ayaka Yukihiro. Chizuru's maternal affection frequently embarrassed him, and while he teased Negi about relationships with female students, others noted the hypocrisy given his own close bonds with Chizuru and Natsumi. His dynamic with Negi evolved from rivalry into deep friendship, serving as an impulsive, battle-driven foil to Negi's reserved intellect. His combat prowess stems from his self-taught Garyū Inugami-ryū style, prioritizing hand-to-hand combat over ranged magic. Key abilities include Spirit Manipulation, summoning inugami (dog spirits) for offense, restraint, or flight via spirit-formed wheels; Transformations into a humanoid "Kuzoku Juuka" form, a full beast "Kuon Eisou" form resembling a black wolf, or partial limb enhancements; and Specialized Techniques like "Kuonbakusaiken" (Howling Burst Knuckle), a spirit-infused punch rivaling Negi's spells, and "Shikukokuroga" (Black Wolf Rapid Air Fang), a high-speed spirit projectile attack. Kotarou faced significant setbacks. A crushing defeat by Albireo Imma in the Mahora Martial Arts Tournament shattered his confidence, fearing Negi would dismiss him as a rival. Kaede Nagase offered training to rebuild his skills. He later accompanied Negi to the Magic World, using age-altering pills to evade recognition. Learning Natsumi was enslaved there, he entered a tournament to free her, Ako Izumi, and Akira Okochi. During the Ostia Festival, he formed a pactio with Natsumi after confessing his love, though she fled before clarifying her feelings. He witnessed the death of Chief, who had protected Natsumi during her enslavement. In later missions, Kotarou prioritized strategic restraint over impulsiveness. Confronting Fate Averruncus during a rescue operation for Asuna and Anya, he acknowledged their power disparity and chose not to engage, avoiding futile sacrifice. This decision underscored his maturation from a brash fighter to a tactician valuing team survival over personal vengeance. His story concludes with an epilogue revealing his marriage to Natsumi Murakami.