Mōryōmaru

"It was a mistake for Naraku to release his heart that day. He even entrusted the Fuyoheki to the Infant, to protect his heart. That's when the Infant had an idea, to create a durable armor of his own. And that armor is Moryomaru, who ate the dead Goryomaru."

- Hakudoshi.

is a composite demon vessel created by Hakudōshi and used by the Infant to combat Naraku.

As far as personal essences go, he is actually the Infant, the physical embodiment of Naraku's heart, and his yōki cannot be detected due to the Fuyōheki, a stone which completely masks the presence of any yōki near it.

Overview
When the Infant decided to replace Naraku, he needed an armor to protect himself with. To this end, Hakudōshi slew a soul-eating demon for the haku (life force) in its belly. He tried patching together the corpses of demons to create prototypes of the armor, but each ended in failure as the haku belonged to humans and the patch-work, malformed bodies were rejected by the haku. Eventually, Hakudōshi discovered that if the form was humanoid, the haku would remain, thus Mōryōmaru was created after several more prototypes.

Mōryōmaru fought against Kōga for his shards, trying to eat him; however, the arrival of Inuyasha's group forced a change in plans, with Hakudōshi redirecting Mōryōmaru's attention to eating Inuyasha. However, the battle didn't go well, and had Mōryōmaru in danger of being destroyed. Because of a telepathic message from the Infant, Hakudōshi protected Mōryōmaru from the Adamant Barrage, using him him to steal the shards of demonic energy from Inuyasha's group, to keep the location of the Fuyōheki safe.

Given to Kanna and the Infant by Hakudōshi, Mōryōmaru was used to attack Goryōmaru's temple in an attempt to eat him to gain an increase in strength; however, after succeeding in devouring the priest's right arm, Mōryōmaru was sealed and used as a replacement arm. Goryōmaru made use of Mōryōmaru's ability to shot demons out of his arm as beams of light, creating Goryo urns for his apprentices to slay demons with. Hakudōshi later beheads Goryōmaru, allowing Mōryōmaru to be freed and finish devouring the priest.

The Infant later places himself in Mōryōmaru, but Naraku manages to lock him inside a cell with statues created by Goryōmaru. He persuaded Kagura into releasing him by promising her the freedom she sought, gaining her assistance in his plan to replace Naraku. He gives her Goryo urns for bandits to use as a distraction for Inuyasha's group. With this occuring, Moryomaru could absorb more demons to increase his strength.

When Kagura betrays him and Hakudōshi by allowing Kohaku, who she was supposed to steal a shard from to increase Mōryōmaru's powers, escape, Mōryōmaru reveals himself to Inuyasha's group. Hakudōshi gives him the shard stolen from Inuyasha's group and he takes off to get Kohaku. He captures Sango, who also chased after him, using her as bait to lure out Kohaku. Using the Infant's ability to read hearts, Mōryōmaru realizes Kohaku regained his memories as they boy decapitates him. He nearly succeeds in taking the shard, only to be stopped by the arrival of the rest of Inuyasha's group. Once they reveal Kagura told them the Infant is inside him, Mōryōmaru is forced to flee on it's orders to get stronger so it can remain safe inside him.

Increasing Powers
As the story progresses, Mōryōmaru begins to increase more and more in power as he absorbs different kinds of yōkai to gain their abilities. He seems to be more adept at this than even Naraku as he sends pieces of his flesh out to gather demon parts. Once he sent his arm to kill a bunch of snake humanoid demons and then absorb them for their vemon, which Kōga witnessed. Here the main focus of the story begins to shift from finding and defeating Naraku, to stopping and destroying the growing Mōryōmaru. Like Naraku, Mōryōmaru rarely appears before his enemies; however, instead of trickery, he often uses other powerful yōkai (whom he plans to devour later) that he influences to fight them. A piece of his flesh is eaten by a venomous demon, allowing to grow in size and power; at this time, the Dragon- scaled Tessaiga proved to be a very useful weapon against the demon and, possibly, even Mōryōmaru himself. Even Naraku believed thag Mōryōmaru faced danger from the blade.

After he revives the corpse of Meiōjū (a turtle-like yōkai) and it regains its armored shell, Mōryōmaru takes control of it and allows Inuyasha to strike Meiōjū with Kongōsōha (Diamond Spear Blast). Though Sesshomaru was trailing Meioju back to him, Naraku surprsingly ordered Byakuya to create a distraction to allow Moryomaru absorb Meioju. Once he's done so, Moryomaru gains a powerful armored shell of his own, along with an equally stong attack. The Kongōsōha are nowhere near as effective when used by Inuyasha due to the lack of the Wind Scar. During the following battle, he nearly defeats an onslaught of most of Naraku's enemies which included Kikyō, Kohaku, Kagome, Inuyasha, Miroku, Sango, Shippō and even Sesshōmaru. During this battle he broke Sesshōmaru's sword, Tōkijin in the process. He only flees after nearly losing one of his jewel shards.

One might speculate that at this time Mōryōmaru had become even more powerful than Naraku himself as he was able to put up a fair fight against so many of his enemies which Naraku wasn't able to do even with the greatest portion of the Shikon no Tama in his possession; however, Naraku is also cowardly and avoids fighting directly. This difference in strength was also noted by Naraku himself in his conversation with Byakuya. In the anime, Moryomaru had no trouble eating Meioju, who was actualy alive in this version, and fought Sesshomaru one-on-one and broke the Tokijin at the cost of a crack in the armor. He gained the Diamond Spears when he caught a moth demon holding Shinta hostage; the Dragon-scaled Tessaiga was used on him personaly instead of the vemonous demon.

Later, after Inuyasha gained the Senki, from a Nikosen, (for his Dragon-Scaled Tessaiga) Naraku sent Kanna to aid Mōryōmaru. He tried to absorb Ginka and Kinka, a pair of conjoined yōkai brothers (sharing an antagonistic relationship with each other not unlike that between Inuyasha and Sesshōmaru), as their blood would bond his armored shell together and prevent Inuyasha's sword from damaging it. Though he succeeds in devouring Ginka, Kinka allowed Inuyasha to absorb him with the Dragon-Scaled Tessaiga, thus giving him the "Flaming Tessaiga". The result is that when Inuyasha used Kinka's power against Mōryōmaru, Ginka's power struck back from within the shell. This greatly weakened Mōryōmaru, and he flees. Soon after, Miroku suggested that Mōryōmaru will discard Ginka's body (since it's become a weakness). In the anime, Mōryōmaru successfully absorbed Ginka and Kinka without any involvement with Kanna or Inuyasha's group, instead Bayakuya merely observes the fight and Sesshōmaru takes Inuyasha's place using the recently reforged Tenseiga.

Confrontation with Naraku
Sometime later, Mōryōmaru became involved in a plot by Naraku, and tried to steal Kōga's jewel shards for himself. However, he found himself at a disadvantage when Inuyasha and Kōga teamed up, with Inuyasha using the Dragon-Scaled Tessaiga's new technique to weaken Mōryōmaru, then Kōga using his Goraishi to break the surface of the armored shell. Even rearranging himself with the diamond spears wasn't enough to save him. Inuyasha broke through into Mōryōmaru's core and saw Akago. Before he could defeat the infant, Inuyasha was flung out when Mōryōmaru grabbed an extra jewel shard from Kai, a younger yōkai-wolf who was also caught up in Naraku's plan. With the shard in hand, Mōryōmaru escaped again, and reaffirmed his plan; to prove that he is superior to Naraku, just as Hakudōshi had intended to do until his death. A few days later, Mōryōmaru was seen to have regenerated, and escaped both Kōga and Kikyō, this time without fighting. Later in chapter 441 of the manga, Naraku ends up running right into Mōryōmaru, who finished recovering from his fight with Inuyasha and Kōga. The evil energy, emanating from these two god-like beings was so strong that when they met the forest below them and all life in it was annihilated by a huge amount of miasma even though they were only headed for each other. Both exchange banter with Naraku saying that Mōryōmaru can't kill him as long as his heart is within Mōryōmaru, while Mōryōmaru says that Naraku can't kill him either for the same reason. Chapter 442 continues with Mōryōmaru continuously destroying Naraku's body with the Kongōsōha that he absorbed from Inuyasha, while Naraku tries to absorb Mōryōmaru back into his flesh and reclaim his heart. Since Naraku can't break through Mōryōmaru's armored shell, he continues to cover Mōryōmaru's body. When it all seemed finished, Mōryōmaru's tentacles pierced the flesh and instead, Naraku's (surprised) face and his flesh are seen absorbed into Mōryōmaru instead. The chapter ends with Mōryōmaru, unharmed, saying "Naraku, I am the victor!” while the members of Inuyasha's group look on in shock.

Mōryōmaru then shifted his focus to taking Kōga and Kohaku's shards to complete the Shikon Jewel. His battle with Kōga and Inuyasha proved to be a stalemate as the Fuyōheki hid his demon vortex from view if his appendages were close to the Infant, and the Goraishi easily shattered his diamonds. Capturing Kōga, Mōryōmaru took off with the Infant furious that the Shikon Jewel wasn't granting Mōryōmaru more power. However, it was at that time that Naraku revealed himself to be alive and well, having allowed Mōryōmaru to swallow him to get passed his armor. When the Infant attempted to "abandon ship", Naraku took over Mōryōmaru and captured him. When Inuyasha cursed Mōryōmaru, Naraku destroyed the haku puppet after absorbing all his useful insides.

Physical Abilities

 * Attacks using tentacles (later on uses tentacles covered in Kongōsōha spears for protection)
 * Has a right hand that acts as a gigantic tentacle made of Kongōsōha spears usually used to impale his opponents
 * He seems to be able make spear-like formations on almost any part of his body
 * He can protect his head from attack, by enlarging the two "hooks" in front of his armor.

Special Abilities

 * Live Body Pieces – Merging pieces of his flesh with other yōkai (and even humans such as Goryōmaru), thus giving him control over them and increasing their regenerative abilities. He often sends pieces of his flesh abroad to scout for new yōkai for him to add into his body.
 * Absorption – Absorbing yōkai and making his body stronger (Later on, he absorbs a yōkai named Meiōjū and gains a nearly impenetrable armor)
 * Yōki Absorption – Absorbing his opponent’s yōki (supernatural energy) and reflecting it back at them or simply consuming it to use as his own.
 * Raimeihō (Thunderclap Cannon) – Fires Black Balls of Lightning, this ability is gained due to the absorption of the Meiōjū.
 * Kongōsōha Spears – While both Inuyasha and Mōryōmaru possess this ability, the strength of this attack depends on the user’s yōki. Since Mōryōmaru doesn't have the Kaze no Kizu (Wound of the Wind) his attack can possibly be weaker than Inuyasha's. This attack can possibly penetrate all barriers, as not a single barrier in the series has been able to withstand its force.
 * Fire/Lightning + Kongōsōha Spears - After swallowing Kinka and Ginka in the anime, Mōryōmaru was challenged by Sesshōmaru. When attacking, Mōryōmaru coated his Kongōsōha spears with the twins' elemental powers.
 * Shōki (poisonous miasma) + Kongōsōha Spears – After he absorbs Naraku, Mōryōmaru is able to upgrade his Kongōsōha attack by launching corrosive Kongōsōha spears infused with shoki. With the resulting damage increase, he was once able to melt entire mountains in one strike.

Trivia

 * In his original Haku form, Mōryōmaru's wings were peach/tan, now, they are bluish-purple.
 * In Episode 6 (FA), it's implied Moryomaru has a small degree of free will, given the Infant told him to stop taunting Naraku and destroy him.