Inosuke Hashibira has a muscular physique and delicate facial features, usually hidden beneath a hollowed-out boar's head mask adapted for sight. His modified Demon Slayer uniform features baggy hakama pants fastened with deer fur and bear hide knee socks, echoing his wilderness origins. Born to an abusive father, he escaped with his mother Kotoha, who sought sanctuary in Doma's cult. Upon discovering Doma consumed his followers, Kotoha fled. Cornered at a cliff, she saved Inosuke by dropping him into a river before Doma devoured her. Wild boars then raised him in the mountains.

This feral childhood left him with limited grasp of human interaction, illiteracy, and frequent name mispronunciation. He displays a short temper, confrontational nature, and boastful personality, often challenging others to prove his strength and demanding praise. This overconfidence drives reckless actions, like attacking the Water Hashira Giyu Tomioka while injured. Early encounters with allies Tanjiro Kamado and Zenitsu Agatsuma involved aggression, as he perceived them as rivals.

His combat prowess relies on self-taught skills. He created Beast Breathing, an original Breathing Style mimicking animal movements, and wields two jagged, chipped Nichirin swords lacking hand guards. Enhanced physical traits include joint dislocation for extended reach, organ shifting to evade fatal wounds, and extreme flexibility enabling backward bends. He also possesses heightened tactile sense for spatial awareness, detecting air vibrations to locate foes. After seeing Tanjiro's Repetitive Action once, he mastered it to boost concentration and stamina. His poison resistance let him survive Upper Rank toxins, though it nullifies medicinal antidotes.

Character growth emerges in key battles. During the Tsuzumi Mansion Arc, he operated alone but shifted to teamwork on Mount Natagumo. After near-fatal wounds from the Father Spider Demon, he acknowledged others' strength and expressed vulnerability by apologizing to Tanjiro for perceived weakness. The Mugen Train Arc showcased his comedic lack of worldly knowledge: he headbutted a train, mistaking it for a "guardian," and experienced a dream sequence leading rabbit versions of Tanjiro ("Ponjiro"), Zenitsu ("Chuitsu"), and Nezuko. His mask's design granted immunity to Enmu's sleep-inducing Blood Demon Art, letting him expose Enmu's neckbone for Tanjiro to sever.

Later arcs solidified his development. In the Entertainment District, he strategically dislocated joints against Upper Rank Six Gyutaro and collaborated with Tanjiro and Zenitsu. Confronting Upper Rank Two Doma in the Infinity Castle Arc, he learned Doma killed his mother, igniting vengeful fury. He coordinated with Kanao Tsuyuri to defeat Doma, utilizing Shinobu Kocho's pre-administered poison. During the final battle against Muzan Kibutsuji, he demonstrated loyalty and camaraderie by mourning fallen comrades and demanding Muzan atone for his crimes.