Mōryōmaru

was a composite yōkai vessel created by Hakudōshi and used by the Infant to combat Naraku.

As far as personal essences went, he was actually the Infant, the physical embodiment of Naraku's heart, and his yōki could not be detected due to the Fuyōheki, a stone which completely masked the presence of any yōki near it.

History
When the Infant decided to replace Naraku, he needed an armor to protect himself with. To this end, Hakudōshi slew a human-souls-eating yōkai 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 patchwork, 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 and his group forced a change in plans, with Hakudōshi redirecting Mōryōmaru's attention to eating Inuyasha. The battle didn't go well, however, and placed Mōryōmaru in danger of being destroyed. Due to a telepathic message from the Infant, Hakudōshi protected Mōryōmaru from the Adamant Barrage, and using him to steal the shards of demonic energy that Miroku was carrying, 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 yōkai out of his arm as beams of light, creating Goryō 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 Goryō urns for bandits to use as a distraction for Inuyasha's group. With this occurring, Mōryōmaru 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 its orders to get stronger so it can remain safe inside him.

Increasing powers
Mōryōmaru began 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 venom, 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 planned 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 that Mōryōmaru faced danger from the blade.

After he revives the corpse of Meiōjū and it regains its armored shell, Mōryōmaru takes control of it and allows Inuyasha to strike Meiōjū with Kongōsōha. Though Sesshōmaru was trailing Meiōjū back to him, Naraku surprisingly ordered Byakuya to create a distraction to allow Mōryōmaru absorb Meiōjū. Once he's done so, Mōryōmaru gains a powerful armored shell of his own, along with an equally strong attack. The Kongōsōha are nowhere near as effective when used by Inuyasha due to the lack of the Kaze no Kizu. 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, Mōryōmaru had no trouble eating Meiōjū, who was actually alive in this version, and fought Sesshōmaru one-on-one and broke the Tōkijin 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 personally instead of the venomous 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 Byakuya 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 the Infant. Before he could defeat the Infant, Inuyasha was flung out when Mōryōmaru grabbed an extra jewel shard from Kai, a younger wolf yōkai 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.

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.

Mōryōmaru continuously destroyed Naraku's body with the Kongōsōha that he absorbed from Inuyasha, while Naraku tried to absorb Mōryōmaru back into his flesh and reclaim his heart. Since Naraku couldn't break through Mōryōmaru's armored shell, he continued 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. Mōryōmaru, unharmed, declared "Naraku, I am the victor!" while the members of Inuyasha's group looked on in shock.

The battle in the anime goes much the same way. Naraku and Mōryōmaru encounter each other over a lush forest, which is immediately reduced to a barren wasteland by the duo's miasma. However, neither appears to be affected by the other's miasma, which implies that their demonic powers are roughly equal. Mōryōmaru announces that he has been expecting Naraku, and Naraku replies that he admires Mōryōmaru's ambition in openly confronting him for the Shikon no Tama. Mōryōmaru, favoring action over banter, proceeds to declare that Naraku's only edge is in the number of shards he possess, and fires a barrage of adamant spears that shatters Naraku's barrier and shreds his body from the neck down. Undaunted, though now only a disembodied head surrounded by the remnants of his body, Naraku proclaims that Mōryōmaru's attempts are in vain; he cannot be killed as long as his heart remains inside of Mōryōmaru. Unfazed in return, Mōryōmaru retorts that Naraku cannot slay him for the exact same reason; he would be committing suicide if he killed the Infant. The Infant, safely ensconced within his armored titan, affirms this, using telepathy to say that "Like it or not, our fates are connected, Naraku. If I die, you die." Naraku then cuts Mōryōmaru off and reveals that the Infant's betrayal came as no surprise to him. Gaining the edge in the verbal match, he goes on to elucidate that the reason the Infant had been released as a helpless baby was so that he wouldn't be able to act against Naraku. He further divulges that the Infant's creation of Mōryōmaru was all according to plan, and that he now "looks forward to devouring him". Discomfited, but nonetheless defiant, Mōryōmaru snorts and rejoins that Naraku cannot talk his way into defeating him. Naraku promptly re-forms his body into an enormous scorpion and sardonically inquires whether Mōryōmaru actually believes that he can defeat him. Proclaiming that the victor will be vindicated, he seizes Mōryōmaru with his multitudinous purple legs and attempts to pierce Mōryōmaru's armor with his pincers and tail. Both efforts are in vain, failing to so much as scratch Meiōjū's nigh-impenetrable shell. After chuckling darkly, Mōryōmaru blasts Naraku away, once again reducing him to tattered shreds of flesh. Declaring that it is over, he subsequently destroys Naraku's head with another hail of adamant. Still undefeated, Naraku switches tack and has the pieces of his flesh coat Mōryōmaru, attempting to absorb him and thus circumvent Mōryōmaru's indestructible armor. However, Mōryōmaru also possesses the ability to absorb others, and retaliates by extending his own tentacles, counter-absorbing Naraku and subsuming Naraku's surprised head into his own body. Floating triumphantly, now having slain his creator, Mōryōmaru exults in his ultimate victory.

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

 * Demon Parts: Possesses similar body-manipulation abilities as Naraku; he can form claws/blades/etc. from his body. Has a right arm that acts as a gigantic tentacle made of Kongōsōha spears, usually used to impale his opponents. He can protect his head from attack, by enlarging the two "hooks" in front of his armor.
 * Tentacles/Spears: He attacks using spear-shaped tentacles (later on uses tentacles covered in Kongōsōha spears for protection).
 * Flight: Mōryōmaru used his bat-like wings to fly, even though it is likely he can levitate without them.

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. His ability to manipulate discrete pieces of himself seems even more refined that that of Naraku himself; he is able to control numerous, widely separated pieces simultaneously, and with a high degree of independency.
 * Regeneration: Much like Hakudōshi and Naraku, Mōryōmaru can regenerate his body indefinitely, since he has no heart. Whether or not the Infant would be affected by Mōryōmaru's body being destroyed is uncertain. Mōryōmaru is never blown to pieces like the other two mentioned, but he is bisected by Kōga, and vaporized from the neck down by Kikyō. Neither instance harms the Infant.
 * Miasma: Mōryōmaru's miasma is used on numerous occasions, in much the same manner as Naraku or Hakudōshi. It seems roughly as potent as the two aforementioned examples'. When Mōryōmaru confronts Naraku, their miasma seems evenly matched, as a gigantic wave sprouts from their meeting point and immediately dissolves all local flora and fauna, but has no adverse effects on either of the two.
 * Absorption: Mōryōmaru wraps his flesh around a target and incorporates its power and abilities into himself. He uses this ability to absorb yōkai and make his body stronger. Most significantly, he absorbs a yōkai named Meiōjū to gain a nearly impenetrable armor. He also absorbs Ginka and Kinka, Inuyasha's Adamant Spears, and even Naraku himself.
 * Yōki Absorption: Absorbing his opponent’s yōki (demonic energy) and reflecting it back at them or simply consuming it to use as his own.
 * Meiōjū's Armor: After absorbing Meiōjū, Mōryōmaru gains an armored shell covering his entire body, save his face, and right arm below the shoulder. He can manipulate the shell as he sees fit, as shown whenever Mōryōmaru sprouts tentacles from his back, absorbs a new demon, or attempts to release the Infant. The shell armor is shown to be even more resilient than the adamant armor employed by Hōsenki, and is capable of deflecting even the strongest of attacks. The most damage it ever takes is a small crack, from Sesshōmaru's Tōkijin, which causes said sword to shatter from the stress.
 * Fires purplish spheres of energy and tendrils of lightning; this ability is gained from the absorption of Meiōjū. It seems roughly equal to the Kaze no Kizu in strength, and can counter Kōga's Goraishi.
 * Kongōsōha Spears:  Mōryōmaru gains this ability from absorbing Inuyasha's Adamant Barrage. He later uses it to great effect for the remainder of his life, most notably against Naraku. This attack can penetrate all barriers, as not a single barrier in the series has been shown as able to withstand its force (excepting Tessaiga's when Inuyasha battles Sesshōmaru).
 * Fire/Lightning with 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. However, their effectiveness is unknown, because Sesshōmaru promptly sucked them into a Meidō Zangetsuha. Mōryōmaru uses this attack again against Kōga, which overpowers his Goraishi blast, but Kōga dodges the fire-coated spears.
 * Shōki (miasma) with Kongōsōha Spears: After he absorbs Naraku, Mōryōmaru is able to upgrade his Kongōsōha attack by launching corrosive Kongōsōha spears infused with shōki. With the resulting increase in potency, he was once able to melt entire mountains in one strike.

Trivia

 * Given Mōryōmaru's performance against Inuyasha, Kikyō, Kōga, and even Sesshōmaru, it can be posited that he has exceeded even Naraku in power, especially once he attains his final form. When he confronts Naraku himself, it is quite clearly shown that, while Naraku's body is repeatedly shredded, Mōryōmaru is completely unscathed, even by Naraku's best efforts.
 * In his original Haku form, Mōryōmaru's wings were peach/tan, now, they are bluish-purple.
 * In Episode 6 (FA), it's implied Mōryōmaru has a small degree of free will, given the Infant told him to stop taunting Naraku and destroy him.

Media appearances
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Manga

 * Chapter 339
 * Chapter 340
 * Chapter 341
 * Chapter 342
 * Chapter 362
 * Chapter 364
 * Chapter 365
 * Chapter 366
 * Chapter 367
 * Chapter 371
 * Chapter 372
 * Chapter 373
 * Chapter 378
 * Chapter 379
 * Chapter 386
 * Chapter 396
 * Chapter 400
 * Chapter 402
 * Chapter 403
 * Chapter 404
 * Chapter 405
 * Chapter 406
 * Chapter 407
 * Chapter 408
 * Chapter 409
 * Chapter 410
 * Chapter 416
 * Chapter 417
 * Chapter 418
 * Chapter 419
 * Chapter 420
 * Chapter 421
 * Chapter 422
 * Chapter 423
 * Chapter 434
 * Chapter 436
 * Chapter 437
 * Chapter 438
 * Chapter 442
 * Chapter 443
 * Chapter 444
 * Chapter 446
 * Chapter 456
 * Chapter 527

Anime
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 * Episode 165
 * Episode 167
 * Episode 1 (FA)
 * Episode 2 (FA)
 * Episode 3 (FA)
 * Episode 4 (FA)
 * Episode 5 (FA)
 * Episode 6 (FA)
 * Episode 20 (FA)