Episode 51 - Inuyasha's Devoured Soul
Sesshomaru visits Bokuseno, a living tree whose branches were used to carve the scabbards for Tetsusaiga and Tenseiga. Bokuseno tells Sesshomaru why Inuyasha was given Tetsusaiga- it is designed to keep his demonic blood from overcoming him. For if this happens often enough he will fly into murderous rages and eventually the pure potency of the blood will be too much for his half-demon body to handle and he will die. While Sango cares for the ailing Miroku who has injested too much poison from Naraku's wasps, Inuyasha and Kagome have a moment to themselves. Eventually they help an old man make his way to a village, but encounter Gatenmaru, a moth demon disguised as a human who is raiding the village. He manages to trap Inuyasha and Miroku inside his venomous cocoon, and tries to take Tetsusaiga for himself. Without Tetsusaiga, Inuyasha begins to undergo another transformation into his full-demon side.
