As a human Hantengu was known to have committed many heinous crimes. Stealing from numerous innocent people and murdering them in various towns and cities all the while claiming that he was innocent and that it wasn't him that committed these crimes. He blamed that his "Hands" were solely to blame for his actions, thus hinting that he was also mentally unstable and possibly delusional due to his claims.
Eventually he was captured by a high-ranked law official magistrate and sentenced to death by decapitation, despite his outrageous claims of innocence that were then silenced by threatening to cut off his "Sinful" hands instead. While imprisoned and awaiting his execution, he was approached by Muzan Kibutsuji who offered to "Help" him after taking pity on his situation. Muzan proceeded to give him some of his blood transforming him into a Demon. After his transformation he escaped his prison and silenced the magistrate who condemned him to death. However with his dying breath, the magistrate told him that killing and silencing him didn't matter because eventually his past sins and actions will see him punished in the future no matter what he did.
Having been summoned to a meeting of the Upper Ranks, Hantengu corrected his colleague Gyokko over the amount of years since they had last met: one hundred and thirteen, a number which unnerved the horned Demon. He cringed as Akaza struck Doma, and bowed as Muzan Kibutsuji arrived. He listened as his leader revealed the death of Gyutaro and berated everyone present for their uselessness, causing the timid Demon to beg for forgiveness. Hantengu then quickly acknowledged Muzan's order for him and Gyokko to head over to an unknown location once the latter confirmed his newfound lead.
The high ranking Demon cringed again as Akaza viciously destroyed Doma's head, only for the former to get his hand lopped off by Kokushibo. He and Gyokko were then transported to their destination by the Biwa Demon.
At the swordsmiths' village, Hantengu crawled on the roof of a building, eager to fulfill their mission to avoid Muzan's wrath. He encountered Tanjiro and Muichiro Tokito shortly thereafter, swiftly avoiding an attack from the latter. He dodged a follow-up attack from Tanjiro, only to be kicked by Nezuko. His head was then severed by another attack from Muichiro, causing him to regenerate into two different Demons: Sekido and Karaku. As Muichiro and Tanjiro attempted to attack these newcomers, Karaku blew Muichiro far into the distance with a single wave of his leaf-like fan. The two then confronted Tanjiro and Nezuko, briefly exchanging biting comments at each other, with Sekido then attacking Tanjiro with a burst of electricity from his shakujō. The two failed to notice Genya approaching them from behind with a gun.
Genya's shot was true, decapitating Sekido but failing to completely do the same to Karaku, much to the latter's amusement. The young Demon Slayer finished the job with his sword, but the two then turned into four. One of the new Demons, reminiscent of a harpy, grabbed Tanjiro by the leg and flew off with him, while the other impaled Genya with a Jūmonji yari. The former congratulated Tanjiro on figuring out their strategy, while the latter commented on Genya's weakness. Tanjiro urged Nezuko to help Genya, prompting his abductor to reprimand him for this, before firing a concussive blast of sound at the Demon Slayer. The harpy-like version of Hantengu was surprised to find that his opponent had hacked off the leg holding him, a head then growing from the severed limb to fire the sound blast at a shocked Tanjiro.
The disembodied head of the harpy-like Hantengu was swiftly cut in two by Tanjiro, swiftly turning into two mouths that fired their sound blasts at him once more. However, their attack power had been lessened due to so many divisions, leading Tanjiro to cut them once more. The main body of the harpy-Hantengu appeared behind the young Demon Slayer, firing another sound blast, which was dodged, but followed up by a vicious claw attack to Tanjiro's chest. The harpy-Hantengu boasted about the sharpness of his claws, promising to carve up the young Demon Slayer, only to discover the youth had sliced his face in two. As Tanjiro prepared a follow-up attack, harpy-Hantengu attempted to fire the sound blast once more, only to have his jaw cut off, the final blow incoming. Elsewhere, Karaku held back a transformed Nezuko, taunting her while Sekido told him to finish her off. The yari-wielding Hantengu, Aizetsu, offered to finish her off, only to discover he couldn't pull his weapon out of Genya, who promptly shot Aizetsu's head into bits.
Sekido reprimanded Aizetsu for this, the yari-wielding Hantengu then pulled his weapon out and slashed Genya across the chest. Regenerating his head, Aizetsu reprimanded his opponent for not dying immediately, and then noticed that Genya had begun to pray. Sekido commanded Aizetsu to crush the scarred Demon Slayer's head, which resulted in the yari being swung at Genya's head. The weapon hit nothing but the floor, the Upper Rank's opponent appearing behind him, swinging his sword at Aizetsu's head. This ambush was foiled by a burst of electricity from Sekido, who was shot at by their highly resilient opponent, much to his frustration. Aizetsu then swung his yari, smashing Genya into a wall. Karaku commented that his allies were having fun, and told Nezuko that he was done with her, driving a foot through her chest.
Karaku then told Sekido to stab and electrocute her until she didn't move anymore, ripping off one of Nezuko's hands off after his speech. She responded with a sudden counterattack, nearly decapitating Karaku and splashing him with her blood. Igniting it with her Demon abilities, she then torn the hand that held his leaf fan and the leg in her chest off. As Sekido demanded to know what Karaku was doing, Nezuko waved the torn arm and fan towards the latter, blowing him into the distance. She attempted to do the same to Sekido, who foiled her attempt by stabbing her in the neck with the butt end of his staff and electrocuting her. Elsewhere, the harpy-Hantengu continued to battle Tanjiro, managing to land a blow while avoiding one from his opponent, and circled around for another attempt. Aizetsu continued to confront Genya, who once again was praying, confused as to how he was still alive and wondering what he was. The Demon Slayer introduced himself, the name of the man who would kill Aizetsu in his place.
As the harpy-Hantengu swooped in for his next attack, he is stabbed through the mouth by Tanjiro, causing the two of them to crash into the building Nezuko and Genya are fighting in. Sekido, still in the process of electrocuting Nezuko, demanded to know what Karaku and Urogi, the harpy-Hantengu, were doing, and manifested a shakujō from his palm. He thrust the weapon at Tanjiro, who blocked it with Urogi's foot. Sekido praised Tanjiro's instincts, as his electricity cannot be transferred through his own cells, and has his tongue cut in half. As his Demon Slayer opponent freed Nezuko from his other shakujō, Sekido attacked the young man from behind, pinning him to the ground. His attack was stopped from doing any further damage by Nezuko, who lit Sekido on fire with her blood technique. Just then, Karaku reappeared, using his fan to demolish part of the building his foes were fighting in, incapacitating both of them. He, Sekido, and Urogi then prepared to finish the pair.
However, their would-be victims recovered quickly, but were knocked down again by an electricity blast from Sekido. Urogi swooped in to attack them, but his attempt was dodged. As the two ran away, Sekido reprimanded Karaku for his slowness, telling him to level the whole building, which the fan Demon quickly accomplished. He then noted that the two no longer had any place to hide. Seeing Tanjiro with a burning blade, Urogi was unfazed and charged in to attack the swordsman as Sekido and Karaku watched. However, Sekido realized that the youth's blade was just like the swordsman's from Muzan's memories, so much so that their very visages seemed to be overlapping. Tanjiro then unleashed Hinokami Kagura: Dragon Sun Halo Head Dance, inflicting grievous injuries to each of the three emotion Demons. A short distance away, Genya had managed to heavily injure Aizetsu, pinning him to a tree with his own yari and ripping his head off.
Each of the Demons hit by Tanjiro's attack reacted differently: Urogi simply screaming in pain, Karaku panicking over his apparent lack of regeneration, and Sekido berating the latter, stating they were still regenerating, but at a much slower pace. Sekido was the first to recover, firing his electricity blast at Tanjiro, Nezuko, and Genya, who were in the process of finding Hantengu's fifth body. Elsewhere, this fifth entity cowered, confident that the other emotion Demons would beat all the "bad guys". Tanjiro directed Genya towards the location of the fifth Hantengu, with Nezuko and himself providing cover for their scarred ally, with an immediate attack launched by Karaku, forcing the youth to grip a nearby tree while Sekido prepared to attack once more. He was attacked by Nezuko, who was immediately pierced by a recovered Aizetsu, who Sekido also attempted to attack, only to have his shakujō hand severed by Tanjiro.
Sekido realized that the youth was improving in ability as the battle progressed, just as he had been told and had observed thus far, noting he experienced explosive growth in critical situations. Urogi's right wing was subsequently severed by Tanjiro, and Aizetsu was grabbed by Nezuko's using both her hands and feet and lit on fire. Seeing this, Sekido desperately looked to see what Karaku was up to. Urogi used his fan to crush Tanjiro into the ground, turning to attack one of the others, only for his fan arm and fan to be split in two by the youth's fiery counterattack. Furious, he stomped on the youth, who continued to give Genya directions on how to find the Upper Rank's fifth body. The two were ultimately successful, the fifth Hantengu cowering at the sight of Genya. The scarred youth shot at the tiny emotion Demon, to no effect, but the miniature Hantengu ran from him regardless. He was pursued by Genya, who swung his blade at the Fear Demon's neck, only for it to break. Another gunshot yielded a similar result, with Sekido attacking Genya from behind almost immediately afterward.
Just as Sekido was about to land the fatal blow, his arm was severed by Tanjiro, causing him to land only a minor blow. As Sekido reeled from the attack, Aizetsu attempted to attack Tanjiro from behind with a flurry of air slashes. His attack was foiled by Genya, who took the brunt of the attack, allowing Tanjiro to land a blow with his fiery blade on the miniature Hantengu, who screamed in agony. As the Fear Demon continued to shriek, a sixth Hantengu appeared from behind Tanjiro, who continued to press his attack. However, the boost he had gotten from Nezuko's blood had ran out, the blade being halted by the miniature-Hantengu's thick neck. Genya shot at the sixth Hantengu, who struck at one of the drums on his body, summoning an amalgamation of tree and dragon, which attacked Tanjiro and flung him up into the sky. Mitsuri arrived and caught Tanjiro, gently allowing him to rest while she fought the hatred clone. The hatred clone wrapped his miniature copy in a protective covering of branches. This new form was revealed to be the result of Sekido absorbing Karaku, Urogi, and Aizetsu, who reacted with a strong glare as Tanjiro told him to stop protecting his Fear counterpart. He asked him if he had a problem with what he was doing, calling the pair of Demon Slayers evil, as the mini Hantengu cowered and trembled in his wooden protection. He answered Tanjiro's question of why he had said they were evil by pointing out their attack on his smaller version, something he called "pure injustice" and something "only a savage would do". He stood impassively as Tanjiro pointed out his misdeeds, promising to cut the Hatred Demon's head off.
In the end, Tanjiro manage to behead him using Hinokami Kagura: Flame Dance. However, the head Tanjiro just cutted was not the real Hantengu, proven as the headless body of Hantengu continues to run away. As the sun is about to rise, Tanjiro finally decides to continue in hia pursuit upon Nezuko sacrifice. Tanjiro eventually locates Hatengu real body inside of Headless Hantengu's heart. Ultimately, Hantengu finally dies after having his torso slashed by Tanjiro. However, Hantengu managed to inform Muzan about Nezuko’s immunity to the sunlight beforehand.