Episode 51

 is the fifty-first episode of InuYasha.

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

Sango is sitting by Miroku, who is ill from the poison of the saimyosho (poison insects) he fought while Sango followed her brother.

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

Sesshomaru 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 Tetsusaiga 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 Tetsusaiga, battles InuYasha. Miroku tries to help InuYasha, but the demon encases them in a poison cocoon with Tetsusaiga - 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 Tetsusaiga, but the sword rejects the demon. The demon 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 isn't healing, 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.