Mōryōmaru
Moryōmaru (魍魎丸) is a character in the anime and manga series InuYasha.
Moryōmaru is Naraku's most powerful minion, although he is working to "replace" Naraku. At first, he is merely a haku (life force) puppet made from yōkai by Hakudōshi. Then he is given to Kanna, who places Akago inside of him (giving the puppet a soul, Naraku's). He is able to absorb the yōki (yōkai "aura/smell") that all yōkai possess and exert (making attacks based solely on yōki energy useless) and convert it into a powerful blast of energy which he releases from his arms (a technique he "lent" to Goryōmaru while he was attached to him).
He is really Akago, the physical embodiment of Naraku's heart, and his yōki cannot be detected due to the Fyōheki, a stone which completely masks the presence of any yōki near it. He has given a bit of trouble to InuYasha and Sesshōmaru, since their attacks (the Kaze no Kizu and blasts from the Tōkijin respectively) are based on yōki, and therefore far from harming him add to Moryōmaru's strength.
Kohaku attempts to kill Moryōmaru after Kagura tells him Moryōmaru is after the Shikon shard in his back since his goal is Naraku's destruction by killing Akago (inside Moryōmaru), but fails, enabling Moryōmaru to nearly steal the shard until Sango comes to his rescue. This in turn enables Moryōmaru to flee from Inuyasha and company.