Episode 51

Inuyasha's Soul, Devoured is the fifty-first episode of the InuYasha anime.

Synopsis

 * 1) Sesshōmaru tracks down an ancient tree demon, Bokusenō, whose boughs were used to create the scabbards of Tessaiga and Tenseiga, and tells him of the change in Inuyasha's blood.
 * 2) Bokusenō tells Sesshōmaru that whenever Inuyasha finds himself in a dire situation, and is without Tessaiga, his yōkai blood takes over; eventually, Inuyasha's human soul will be completely devoured by his yōkai blood and he will turn into a fearsome beast who only lives to fight, and he will continue to fight until he dies.
 * 3) Inuyasha and his friends encounter a moth yōkai called Gatenmaru, who has been posing as a human leader of a group of bandits; Inuyasha and Miroku are trapped in Gatenmaru's poison cocoon, where Inuyasha has been separated from Tessaiga.

Summary
Sesshōmaru, Jaken and Rin walk through the forest. A voice welcomes Sesshōmaru, and says he expects Sesshōmaru has come to talk about the swords.

Sango is sitting by Miroku, who is ill from the poison of the Saimyōshō he fought while Sango followed her brother.

Bokusenō, a 2000 year old magnolia tree demon, speaks of the Tessaiga and the Tenseiga. The sheaths of the swords come from this tree.

Sesshōmaru asks about Inuyasha, and how he has changed sometimes into a pure demon. The tree demon explains that Inuyasha is sometimes overcome by his demon blood to preserve his life. However the more often Inuyasha transforms, the more the blood will control him, eventually turning him into a mindless killer. The Great Dog Demon, knowing this, gave the Tessaiga to Inuyasha, to protect him from his blood.

As Inuyasha, Kagome, Miroku, and Sango are traveling, they come upon a village under attack by bandits, with a demon among them. The demon, desiring Tessaiga, battles Inuyasha, dousing him in toxic dust and slashing him across the torso with his battle-axe. Miroku tries to help Inuyasha, but the demon encases them in a poison cocoon with Tessaiga - transformed into a rusty sword again - trapped outside. Miroku created a barrier within the cocoon, but Inuyasha is poisoned and cannot move.

The demon - Gatenmaru - tries to claim Tessaiga, but the sword rejects the demon. Gatenmaru realizes that Inuyasha's human blood must allow him to wield the blade.

Worried about Miroku and Inuyasha, Sango and Kagome head toward the village. Inuyasha's wound, rather than healing, is opening further due to the venomous dust, and Miroku worries that his barrier can't last forever. As the barrier weakens, and Inuyasha's wounds get worse, his demon half begins to take control.