Serpent Hashira Obanai Iguro carries a legacy of blood and guilt. Born the first male in his clan for 370 years, his family worshipped a serpentine demon with a woman's torso and snake's tail, sacrificing newborns for stolen riches. His rare gender and heterochromia condemned him. Confined from infancy and overfed for sacrifice, the demon observed him nightly, instilling terror. Presented at twelve, the demon ordered his mouth slit ear-to-ear to match her own and drank his blood. Obanai escaped, chipping cage bars with a stolen hairpin, aided only by a small white snake, Kaburamaru, who became his constant companion. During his flight, the demon slaughtered nearly all fifty clan members. His sole surviving cousin blamed him, deepening his guilt and self-loathing, driving him to join the Demon Slayer Corps. He seeks redemption by eradicating demons and atoning for his "tainted" bloodline. Obanai exhibits a strict, distrustful, and harsh demeanor, especially toward demons and rule-breakers. He initially demanded execution for Tanjiro Kamado and Nezuko Kamado due to Nezuko's demon nature. He harbors deep gynophobia, avoiding women except Mitsuri Kanroji, the Love Hashira, toward whom he feels profound affection. He writes her letters and gifts her items like green-striped socks but refrains from confessing, believing his corrupted blood makes him unworthy of happiness. He vows confession only in a future life after reincarnation. His respect is reserved for Kagaya Ubuyashiki, the Corps leader, and Gyomei Himejima, the Stone Hashira, whose strength he admires. He shares a bond with Tengen Uzui over traumatic pasts and considers Sanemi Shinazugawa a friend, aligning with their rigid views on demon extermination. He clashes with Giyu Tomioka, viewing him as aloof and unfit. Physically, Obanai stands 162 cm tall with a slender build. He possesses heterochromatic eyes—turquoise left, yellow right with impaired vision—and conceals his scarred mouth with bandages. He wears the standard uniform under a black-and-white striped haori and carries Kaburamaru, who aids his limited sight. His Serpent Breathing fighting style mimics a serpent's twisting movements, utilizing a unique wavy, serpentine Nichirin Sword. Despite ranking as the second-weakest Hashira physically after Shinobu Kocho, his combat skill is exceptional. In the final battle against Muzan Kibutsuji, he awakens his Demon Slayer Mark, manifesting snake-like patterns on his arm and chest, enhancing his speed and reflexes. He also achieves a Crimson Red Nichirin Blade through intense grip strength, temporarily hindering demon regeneration. Blinded in this battle, he fights on using Kaburamaru and a talisman for spatial awareness, sustaining severe injuries. During the Entertainment District Arc, Obanai arrives after Upper Six demons Daki and Gyutaro's defeat. He tersely congratulates Tengen Uzui but notes they were the weakest Upper Ranks. When Tengen announces retirement, Obanai angrily insists he continue, citing the Corps' need for experienced Hashira and dismissing newer recruits as weak. Tengen counters by highlighting Tanjiro Kamado's potential, surprising Obanai, underscoring his pragmatic yet inflexible stance on hierarchy. Later, Obanai participates in the Hashira Training Program, conducting rigorous sword skill revisions. He ties lower-ranking slayers to walls as punishment for perceived weakness, believing inadequacy endangers the Corps. Fighting in the Infinity Castle and against Muzan, he battles Upper Rank Four Nakime. Mortally wounded and blinded, he locates the dying Mitsuri, covers her with his haori, and expresses his wish to meet her in their next life, implying his unresolved love. In the "Kimetsu Academy" spin-off, he is reimagined as a chemistry teacher who wears a mask due to his "girl allergy," retains Kaburamaru, and maintains his reserved yet subtly caring nature, helping students choose gifts. His abilities include prolonged fasting—up to three days without food—stemming from childhood trauma. His uniform is crafted from durable, fire-resistant fabric. Quotes like "I do not trust. I hate demons" encapsulate his philosophy. Despite his stern exterior, his actions reveal a commitment to protecting others and a deep-seated desire for redemption.