Demon Slayers vs Tanjiro Kamado

Tanjiro Kamado vs Demon Slayers is the final battle against Demons in the Kimetsu no Yaiba universe, taking place outside the destroyed Infinity Castle. It focuses on the battle between the newly demonized Tanjiro Kamado against the surviving members of the Demon Slayer Corps.

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 evolves his Demon form and grows bone appendages similar to Muzan's.

Nezuko keeps begging to Tanjiro to not lose himself from Muzan but Tanjiro keeps mindlessly attacking the Demon Slayer Corps, swinging one of his bone appendages towards Zenitsu. Giyu saves Zenitsu and a few Kakushi using the Water Breathing: Fourth Form - Striking Tide. 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 Flower Breathing: Final Form - Equinoctial Vermilion Eye on her left eye and approaches Tanjiro to inject him with the medicine, getting struck by one of Tanjiro's bone appendages in the process. In Tanjiro's mind, 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 fades from Tanjiro's subconscious, finally defeated for good.

Aftermath
Tanjiro later awakens as he's surrounded by a tearful Nezuko and the rest of the Demon Slayer Corps, gleefully welcoming him back. Kanao is later shown to be alive despite her injuries and she manages to share a heartful smile to Tanjiro, which he reciprocates. On the other hand, Yushiro, who is currently hiding from the sun, manages to find Tamayo's hairpin. He tearfully comments that the long-lasting battle between the Demon Slayer Corps and Muzan has come to a close.

Three months later, Kiriya announces that the Demon Slayer Corps will be officially disbanded and thanked the remaining active Hashira, Sanemi and Giyu, for their hard work. In turn, both Hashira thanked the Ubuyashiki family for giving them the chance to avenge their loved ones, which greatly moved Kiriya. Meanwhile, Tanjiro is recovering in the Butterfly Estate, and commented that now Muzan's control over him are gone, his regenerated arm has heavily aged and lost its sensation from the elbow downwards while is regenerated eye is now blinded. However, Nezuko reassures him that this is for the best. After Tanjiro, Zenitsu and Inosuke were fully healed, they all moved to Tanjiro's old house and lived happily.

At one point before its disbandment, the Demon Slayer Corps members and their relatives took a commemorative photo together. The photo, along with Yoriichi Tsugikuni's Hanafuda earrings and Tanjiro's Nichirin Blade with Kyojuro Rengoku's hilt still exist in the present day, under the care of Kamado household.