Demon Slayers vs Tanjiro Kamado

Prologue
As Muzan Kibutsuji lays dying, he transforms Tanjiro Kamado into a Demon and transfers all of his memories to the young Demon Slayer in a desperate effort to preserve himself. Muzan entrusts Tanjiro with wiping out the Demon Slayers and believes that Tanjiro would, like his sister, conquer the sun.

Battle
Upon becoming a Demon, Tanjiro recovers from the poison that caused the growth on his face and regenerates his lost arm and eye. As Muzan had predicted, Tanjiro shows resistance to sunlight when he faces off against Giyu Tomioka. He goes to attack Inosuke Hashibira, only to be embraced by a panicking and saddened Nezuko. Nezuko tearfully begs her brother to stop so they could return back home, and Tanjiro manages to temporarily calm himself down after he unconsciously bites Nezuko's shoulder. However, as Inosuke lands several punches to Tanjiro in frustration, Tanjiro further evolvies his Demon form and grows bone appendages similar to Muzan's.

Tanjiro begins generating an energy ball to direct towards the Demon Slayers, however, his attack is intercepted by Nezuko and severely damages her arm. A powerless Zenitsu cries out to Tanjiro, horrified at the thought of Nezuko dying by the hands of her brother. As Giyu and an onlooking Yushiro try to find a way to stop Tanjiro, Kanao Tsuyuri arrives, bringing a vial of the humanification medicine.

Kanao uses Breath of Flower Final Form: Equinoctial Vermilion Eye to approach Tanjiro and inject him with the medicine, getting struck by one of Tanjiro bone appendages in the process. In Tanjiro's consciousness, Muzan tries to convince him to let himself be consumed by the desire of becoming the ultimate being. Tanjiro vehemently refuses Muzan's offer and several hands belonging to his loved ones, both deceased and alive, rise from the ground and through the Wisteria flowers to push and reach out for him. Tanjiro accepts their grasps and is brought back to reality with his humanity restored. Muzan is left alone in Tanjiro subconsciousness, finally defeated for good.