S01E51: Inuyasha's Soul, Devoured

Sesshomaru learns from the wise tree-demon, Boku'seno that when Inuyasha transforms into a demon, his demon blood takes full control turning him into a mindless killing machine. Elsewhere, Inuyasha and the others arrive at a village that is ruthlessly being held under the control of the Moth Demon, Gatenmaru and his band of thieves.