The Fuyōheki is a magical item from the InuYasha manga series.
Originally in the possession of Gakusanjin, it is a stone that masks the presence of yōki (yōkai energy). In the anime, Naraku stole it in order to mask the demonic aura of Akago, who is the heart of him and Hakudōshi. InuYasha, Kagome, Miroku, Sango, and Shippo came across Gakusanjin when acting on the tip of a villager. They would have met their deaths if InuYasha did not inquire whether Gakusanjin was conspiring with Naraku, as well as the entire party's hatred for Naraku.
During the encounter, Gakusanjin told the team that the Fuyōheki dissipated demon auras, and allowed him to remain in a slumber. Gakusanjin never completely trusted them, but gave them crystals that contained his own demonic aura. He told them that the crystals were green when surrounded by their demonic aura, but would look like pure white crystals in the presencec of the Fuyōheki.
Once, the crystals turned white because they were near the cave in which Kan'na was hiding Akago and the Fuyōheki. Kagura came upon them and attempted to kill Akago, but failed, as Kan'na took the infant into her own hands and ran off the cliff on which the cave existed.
Meanwhile, everyone was searching for the Fuyōheki. When Kanna jumped off the cliff, she disappeared in a fog. After her dissapearnce, the reader sees a brief shot of Kagura plucking a feather from her hair and using it to summon the large feather upon which she flies. The camera returns to the team, who are somewhat angered by the fact that Naraku has again thwarted them, because they do not know that it was Kanna who was guarding Akago and the Fuyōheki.
Circa #335 it was stolen by Naraku. The Fuyōheki was then 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. After the destruction of Mōryōmaru, in a failed attempt to destroy Naraku, Miroku sucked it into his Kazaana.
Fuyōheki is translated as "seal (fu) enchanted (yō) stone (seki or heki)" or "the demon-sealing stone".