Episode 108

The Secret of the Pure Light is 108th episode of the InuYasha anime.

Plot
While Kikyo, intrigued, stay near Doctor Suikotsu to unravel the mystery of the purity of his Shikon shard, InuYasha sits by a fire with his friends, swearing he will kill each and every one of the band of seven. When he meets Suikotsu, he pegs him at once as one of the seven, due to the characteristic graveyard scent, but his manners are so different from those expected of a murderous mercenary, young children make him a shield of their bodies. Miroku tells InuYasha to desist, saying that maybe there is a mistake. Kagome is unsure, due to the purity of the shard. Farther away, the remaining members of the band of seven attack the village. Suikotsu rushes to the help of the villagers, joined by Kikyo. The band tells Suikotsu to "snap out of it", which he doesn't seem to understand, until Jakotsu hurts him, spilling blood over him. To the astonishment of InuYasha, his friends and Kikyo, he then attack the children, entirely transformed, and introduce himself as Suikotsu of the band of seven, seemingly with a personality disorder.

Trivia

 * When Inuyasha lost the Tessaiga, he didn't transform into a demon. This could be due to the power of the Mt. Hakurei, which blocked his yōkai spirit.