Gakusanjin

Gakusanjin is a character in the manga and anime series Inuyasha. He first appears in chapter 336 of the original (japanese) manga.

Gakusanjin is a mountain yōkai who used the Fuyōheki, a stone that masked the presence of yōki (yōkai energy), to pass unnoticed and avoid confrontations.

Circa #335 his Fuyōheki was stolen by Naraku or his agents (possibly Hakudōshi). Now perceptible, Gakusanjin was forced to leave his usual resting place and move in an attempt to recover the Fuyōheki. He learned of Naraku from InuYasha's group and lent them yōki-imbued cristals that they could use to detect the proximity of the Fuyōheki.

He was shortly after killed by Goryōmaru child protegeés, who did not bother to investigate whether he was a hostile yōkai or not. The Fuyōheki was given by Naraku himself to Akago in order to mask him (and Naraku's heart inside him) completely from Naraku's enemies. It was later absorbed (along with Akago himself) by Mōryōmaru.