Inosuke Hashibira/Synopsis

History
Inosuke was raised by boars for most of his life before the Final Selection. It was revealed later that he was born into a family with an abusive father and escaped from his father with his mother.

Afterwards, Inosuke—who was still an infant at the time, his mother were taken in by Doma into his Paradise Faith cult. Kotoha loved to sing to Inosuke but would apparently change the song lyrics each time. However, after finding out that Doma ate his worshippers, Kotoha fled with her son. Running aimlessly for a human village, Kotoha eventually ended up at the top of a cliff. Seeing no escape route, she made a last-ditch effort to save Inosuke by dropping him into the river below the cliff. She was then devoured by Doma. Later on, Inosuke was discovered and raised by boars.

Synopsis
Before Final Selection, a Demon Slayer bumps into Inosuke in the latter's mountain. The two competed to see who was stronger, with Inosuke being the victor and taking the Slayer's weapon as a reward. As a result, Inosuke learns more about the Demons and decides to join the Demon Slayer Corps.

Final Selection Arc
While Inosuke does participate in the Final Selection at Mt. Fujikasane, he is off-screen for the entirety of the arc. His presence is hinted by Kagaya Ubuyashiki, when a crow tells him the results of the selection.

Tsuzumi Mansion Arc
Inosuke had wandered into the Kyogai's Drum house presumably looking for a demon to kill to serve as his "catalyst" to becoming stronger, but due to the nature of Kyogai's blood demon arts, he ended up trapped for 3 days. He first appears when Zenitsu and Shoichi are searching for an exit, having been separated from Tanjiro and Teruko. Zenitsu slides open a door which he believed was the exit, and desperately opens another when the first door fails. Behind that door is Inosuke, who immediately hurtles out and knocks down another door before running down the opened corridor. Zenitsu is left shakened, with Shoichi wordlessly judging him.

Natagumo Mountain Arc
After resting at the Wisteria House due to their injuries, they are summoned by Tanjiro's crow to head to Natagumo Mountain. Inosuke and Tanjiro rushes into the mountain, with Zenitsu lagging behind due to his fear, after seeing a fellow Demon Slayer asking for help. The Demon Slayer was then pulled backwards, back into the forest. After witnessing that, Inosuke acts as the vanguard and orders Tanjiro and Zenitsu to follow him. Tanjiro follows Inosuke while Zenitsu stays near the mountain, refusing to enter.

After meeting with an another Demon Slayer who was hiding from the Demons, Inosuke and Tanjiro understands the situation present that the Demon Slayers began to kill each other after entering the woods, due to a Demon's blood art making them into puppets that can be controlled. After trying their best to not kill the controlled Demon Slayers, Inosuke uses his Beast Breathing, Seventh Form: Spatial Awareness to find the demon known as 'Mother'. Inosuke and Tanjiro manages to hang the controlled Demon Slayers onto the trees to immobilize them, however, the demon controlling them twists their necks, killing them after they are immobilized. With heavy hearts, they proceed to the demon's location, but was stopped by a headless puppet controlled by the demon.

During the battle with the headless puppet, Inosuke's hastiness gets him injured and almost killed. Thankfully, Tanjiro saves him and encourages Inosuke to fight alongside him. Even though Inosuke was unwilling to, he however, thanks to Tanjiro's instructions, is able to cut the headless puppet diagonally. Inosuke is very competitive with Tanjiro, thinking he can do everything Tanjiro can. Tanjiro defeats the demon known as 'Mother' and Inosuke is severely wounded, although he is not willing to admit to it.

Tanjiro tries to get Inosuke to get down the mountain and he refuses. They catch a glimpse of a demon girl, who Tanjiro could not smell due to the putrid scent surrounding the mountains. The demon girl calls for another demon called 'Father', who is a large man with the face of a spider. He is a strong demon, though not a Twelve Kizuki, and Inosuke is staggering due to blood loss. Tanjiro is sent flying away due to the demon's strength and shouts for Inosuke to not die at all costs. Inosuke manages to cut the demon's arm, making him climb up to trees to shed his skin and show an even larger spider-like body. Inosuke tries to behead the demon with his Beast Breathing, Third Fang: Devour, but his blades break and he was strangled by the demon. Luckily, Giyu shows up and kills 'Father' with the Water Breathing, Fourth Form: Striking Tide, saving Inosuke's life.

Inosuke, despite his wounds, tries to challenge Giyu but ends up getting tied up. This makes Inosuke's confidence in himself drop and makes him think he is not as good as he thinks he is. After the battle, Inosuke is then released from the ropes by the Kakushi, the squad that deals with the aftermath of demon battles.

Rehabilitation Training Arc
Due to the injuries he sustained from the 'Father', Inosuke's throat became mangled, so he was taken to the Butterfly Mansion to heal alongside Tanjiro and Zenitsu, who went up the mountain behind them and was almost turned into a spider. Humiliated at how he lost, he apologizes to Tanjiro for being so weak.

Infinity Castle Arc
As Doma sends his Blood Demon Art, Scattering Lotuses at Kanao, at that moment, Inosuke suddenly breaks through the ceiling of the room, protecting Kanao from Doma's attack with his Beast Breathing, Fifth Fang: Crazy Cutting. He looks at Doma's eyes and notices that he's Upper Rank 2, which he screams out, happily shouting that if he beats the Demon he'll become a Hashira and asking Kanao what his Hashira title should be. Inosuke notices Kanao's beaten-up face, and asks, surprised, what had happened, saying that Shinobu will get mad if she finds her Tsuguko in that state. Kanao remains silent, the boar-headed Demon Slayer comes to a realization and asks her if Shinobu is dead, to which Doma replies that she isn't; she will live inside of him for all eternity because he has "saved" her from her pain and suffering. Inosuke recalls Shinobu's kindness to him, and vows to Doma that he'll kill him as he rushes towards the Upper Rank with his Beast Breathing, Fourth Fang: Slice 'n' Dice.

Kanao shouts out a warning to him not to breathe in Doma's cold air as the Demon remarks on how messed-up his technique is. Doma attempts to slice off Inosuke's head with one of his fans, but the Demon Slayer flips away from him, launching himself from the flat edge of the fan and landing next to Kanao. He hands her her blade, which he had taken back from Doma, and tells her never to let go of it again. Doma smiles and compliments Inosuke's speed as he jumps towards him, and the two swiftly engage in quick combat, launching Breath Styles and Blood Demon Arts at each other at alarming rates. Inosuke kicks Doma in the stomach, sending him skidding backwards as he dislocates the joints in his right arm and prepares to swing his sword at the Upper Rank's neck. He misjudges his swing and instead slices through Doma's eyes with his Beast Breathing, Ninth Fang: Extending Bendy Slash, and the Demon laughs at his unusual technique as his joints relocate.

Doma calls Inosuke messed-up and says that he's never met a kid like him before despite his long lifespan, to which the Demon Slayer replies that that's obvious, since he is the great Inosuke. At an incredible speed, Doma launches himself forward and snatches his mask from his head as he's speaking, Inosuke, enraged, yells at him to give it back. The Demon notices his face, and says he remembers Inosuke from somewhere, asking him if they'd met before. Inosuke responds that they hadn't as he would remember meeting someone like Doma, but the Upper Rank insists that they have, proceeding to stick his finger through his skull and into his brain to try and jog his memories. Doma says that he knew Inosuke's mother, as his cult took her in, but Inosuke denies that he has a mother since he was raised by boars. Doma laughs and says that he must have a human mother since he's a human, and Inosuke shouts at him to quit spouting lies and give him back his boar mask, rushing in to attack the Demon again with Beast Breathing, Sixth Fang: Palisade Bite. His torso is slashed twice by Doma's fans, who smiles slyly and tells him not to interrupt before sending him flying back to Kanao with his ice.

Doma then tells the story of Kotoha, Inosuke's mother, and how she and her baby son joined Doma's cult only to end up running away after she realized the Demon was eating his followers. He explains that she met her demise by Doma's hands, who still believes he is saving her from her abusive household by eating her, but dropped her son off a cliff before the Demon's attack in the hope that he would survive. Memories of her begin to come back to Inosuke, who recalls the song she used to sing to him. Doma calls Kotoha stupid and unfortunate, saying that there isn't a happy moment in her life, and Inosuke, now enraged, thanks Doma for allowing him to remember this story and promises to not only to kill him for what he did to Kotoha and Shinobu, but to put him through hell beforehand.

Doma smiles again, and tells Inosuke that there is no heaven or hell in this world since they're nothing but fantasies created as a coping mechanism for weak humans. Inosuke shouts that he doesn't care if there's no hell because he can just make one himself, and tells Doma not to talk about his mother like she is unhappy.

The Demon sends his Freezing Clouds at Inosuke, which he blows away with Beast Breathing, Tenth Fang: Whirling Fangs as Kanao prepares to use another Breath Style to attack him from behind. Doma bats her away with one of his fans and moves away. Inosuke yells at him to get back down so they can continue fighting. He replies that he can't, since Akaza has been defeated and he doesn't have time to play anymore, and uses his Blood Demon Art, Crystalline Divine Child to create smaller clones of himself for Inosuke and Kanao to fight instead. The clones attack the Demon Slayer duo with Doma's techniques as the real Doma starts to walk away, the clones using his Blood Demon Art, Scattering Lotuses, Frozen Lotus and Cold White Princesses attacks to hold the duo back. Now at the exit, Doma thinks about how Inosuke has managed to avoid breathing in the icy air from his techniques, and takes note of his sharp senses, saying he will make sure to remember him. He spectates their battle for a few seconds, observing how they use each technique so that he'll be able to kill them quickly the next time they fight, and then turns back towards the door.

Doma decides to create three more clones to let loose around the castle in order to kill the rest of the Demon Slayers there, and overhears Kanao shouting to Inosuke that they have to hold their ground just a little longer against the crystal children. He wonders what this could mean, but then dismisses it and begins to reach for the door handle. Suddenly, Doma's face begins to melt. He drops to the floor, one of his arms snapping off, and his crystal children begin to crack and disintegrate as he wonders what's happening. Inosuke asks if it's a trap but Kanao, having been informed prior to the battle of Shinobu's plan to kill Doma, tells him that it isn't, and that the Demon is being melted by the poison Shinobu had in her body when he consumed her. She tells Inosuke to aim for his neck to finish him off, and, in a panic, Doma plays his final and most powerful card, Blood Demon Art, Rime — Water Lily Bodhisattva.

Doma's ice Bodhisattva statue slams down its hand on the floor of the room, creating a small earthquake that sends Inosuke and Kanao up into the air. Kanao notes that his technique lacks precision, and is clearly the Demon's last effort to protect himself with the little energy he had left, deciding to use her final form, Flower Breathing, Final Form: Equinoctial Vermilion Eye to try and break through him. Doma's statue grabs Inosuke in one of its hands as Kanao leaps towards the Upper Rank, hitting her blade against his neck. She is unable to cut it, so Inosuke, on the spot, comes up with and uses Beast Breathing, Sudden Throwing Strike to hurl his blades at Kanao's to give it the extra strength needed to cut Doma's neck. They succeed in beheading him, Upper Rank Two and his statue begin to disintegrate.

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