In the Demon Slayer series, a significant turning point occurs when Tanjiro Kamado, the series’ protagonist, undergoes a transformation into a demon. However, this event unfolds in the manga’s final arc and has not yet been depicted in the anime adaptation, which is still ongoing.
In Chapter 201 of the Demon Slayer manga, following an intense battle with the Demon King Muzan, Tanjiro sustains severe injuries that would inevitably lead to his death. Seizing the opportunity presented by his impending demise, Muzan, who is also on the brink of death, utilizes his remaining powers to enact his long-planned scheme: transforming Tanjiro into a demon.
Muzan’s intent behind turning Tanjiro into a demon was to create the most powerful demon ever known, surpassing even Muzan himself. Due to the unique bloodline of Tanjiro’s family, both Tanjiro and his sister, Nezuko, possess an ability that allows them to withstand the effects of sunlight, unlike other demons.
This transformation ultimately leads to Tanjiro becoming the Demon King and consequently becomes an adversary of the Demon Slayer Corps. Muzan’s desire was for his will to persist through demon-Tanjiro, aiming to bring an end to humanity even after his own demise.
Fortunately, Tanjiro’s reign as the Demon King is short-lived. Through the use of medicine crafted with Wisteria Flowers, Tanjiro is reverted back to his human form, ending his tenure as the demon king and thwarting Muzan’s plans for his legacy to endure beyond death.
This pivotal moment in the manga’s conclusion showcases Tanjiro’s struggle with his transformation into a demon and the subsequent efforts to restore his humanity, contributing to the depth and complexity of the series’ narrative.