Magatsuhi

is indirectly the real antagonist of the entire story, who caused all events that include both the birth and actions of Naraku.

He is the incredibly powerful dragon yōkai who killed Midoriko and whose soul with whom she continuously battles inside the Shikon Jewel. He was created by numerous minor demons who formed into one demon in order to kill Midoriko. His true form is much more monstrous.

Origins
Magatsuhi is the dragon demon who fought and died with the ancient priestess Midoriko hundreds of years before the events of the series, during the Heian Period of Japan, when the shoguns served as de facto rulers over most of Japan. He was created when many yōkai possessed a mortal man who secretly desired Midoriko, similar to how Onigumo loved Kikyo and created Naraku.

However, as opposed to Naraku, he is a full demon and not an hanyō. In fact, while Onigumo had been devoured by demons and his soul was used as an adhesive, the man who loved Midoriko was only incorporated on the base of the dragon's neck. Therefore, contrary to Naraku, he is completely devoid of human feelings.

Defeat & Death
The final battle lasted for seven days and nights and eventually Magatsuhi captured Midoriko in his jaws. Midoriko, in one final attempt to defeat Magatsuhi, pulled his soul into her body - fusing it with her own soul - and then expelled them both simultaneously along with her heart.

Both Magatsuhi and Midoriko died, but their souls combined to give birth to the Shikon no Tama. Midoriko and Magatsuhi remained imprisoned within the Jewel and continued to battle ever since.

During the story
Magatsuhi is first seen in manga chapter 89 as the mummified corpse of an unnamed but massive demon.

In the anime versione, the souls of the demons that formed him appear from the Shikon Jewel when a fragment of it gets near his stone body, attempting to escape and revive. Kirara transforms to fight them, and they combine into a ghostly Magatsuhi, who wraps his tail around Kirara and attempts to kill her before Inuyasha and the soul of Midoriko fight him off, and he remains inside the Jewel for the time being.

Reborn
Later in the manga, the demon's name is revealed to be Magatsuhi, and Naraku helps him to manifest in physical form so that Magatsuhi can help him to complete the Shikon Jewel. Magatsuhi seems to fear Kagome's spiritual power and seals away her true strengths to prevent her from purifying him. Magatsuhi's first mission after coming to life is to defile and obtain Kohaku's shard but he is obstructed by Sesshōmaru, whose sword Magatsuhi fears, as it can kill him. Magatsuhi flees after being injured by Bakusaiga in the fight (having lost the flesh which Naraku lent him), and along with Naraku tricks Sesshōmaru into leaving Kohaku alone with a fake Magatsuhi.



He succeeds in kidnapping Kohaku, made unconscious by Magatsuhi's defilement of his shard, and severely injures Miroku and Sango who tried to stop the demon. He remained in control of Kohaku, tormenting the boy with visions of his past, until Kohaku managed to awaken and break free of Magatsuhi. Kohaku then attempted to drive the demon from his body, even at the cost of his own life. Magatsuhi curses him and fights back until being slashed by Sesshōmaru, who has returned after realizing he was tricked. Sesshōmaru attempts to kill Magatsuhi but he escapes at the last moment, having hidden his essence in Miroku, who he poisoned.



Magatsuhi then appears inside Naraku's enormous spider body in the final battle, possessing Inuyasha and trying to kill Rin and Kagome. Sesshōmaru mocks him, taunting Inuyasha was the worst person to possess and Magatsuhi finds Inuyasha fighting back at his control. He is driven from Inuyasha's body and after trying to take over Kagome, but Inuyasha stopped him with Dragon-scaled Tessaiga and is apparently killed by Sesshōmaru with Tenseiga.

Inside the Shikon Jewel
However, Magatsuhi is not completely dead, as he is still connected to the Sacred Jewel, and his spirit is still in combat with Midoriko inside the Jewel. Then only the unified consciousness of Magatsuhi (like how Naraku is in control of the demons that made up his body) was destroyed by Sesshōmaru.



Inuyasha inadvertently dives into the Jewel and encounters a giant dragon-like demon. Possibly unknown to Inuyasha, this is the true Magatsuhi, still living and battling within the Jewel. Inuyasha slices him immediately with the Wind Scar, and he is split into the many demons that formed him.

Magatsuhi states that Inuyasha does not need to keep searching for Kagome, and says that she'll be here soon enough. He also states that if Kagome were to make a selfish wish on the Shikon Jewel, Kagome would replace Midoriko in the eternal fight in the Jewel and Naraku would replace him. In the manga, but not in the anime version, his desire expressed by Naraku dissolved forever Midoriko's soul in order to prepare the place for Kagome.

Magatsuhi's true plan is finally realized. During the entire story, he had always manipulated Naraku through the Jewel in order to replace himself with Naraku, thus freeing himself from the Jewel in the process, leaving him free to unleash total destruction upon the world once again, with no one to stop him.

Final Death
Inuyasha refuses to believe Magatsuhi, and proceeds to attack the demons that form him in an attempt to reach Kagome in the Meidō outside the Jewel and save her.

In the manga, Magatsuhi and Naraku were destroyed forever by Inuyasha when he cuts the point of light in the darkness inside the Shikon Jewel with Meidō Zangetsuha, which is the key left by Kikyo before dying to kill Naraku and destroy the jewelry evil. In fact, with Inuyasha's attack at this very point, the purity of the Jewel called Naohi annihilates the evil corrupting presence within it, then the Jewel's shimmering and voice completely stopped. The rest of the Jewel breaks and then disappears when Kagome makes the right wish for it to be taken out of existence.

Instead, in the anime version, when Kagome makes the right wish, Magatsuhi (the demons that form him) is enveloped in light, along with Midoriko and Naraku, finally putting an end to his, the Jewel's, and Naraku's evil. Inuyasha and Kagome are transported back to earthen ground.

True Rule
By the end of the series, it is clear that Magatsuhi is indirectly responsible for almost everything terrible that happened in the whole story. Ultimately, he is the true (along with the Jewel itself) and most dangerous villain from the beginning, as he is the indirect reason the Shikon Jewel exists at all, having forced Midoriko to create it in her death, and so everything going wrong throughout the entire story, as a result of the many struggles for the Jewel, or the Jewel's own plans to keep the battles between good and evil going inside of it, ultimately leads back to him and his desire to destroy Midoriko.

This revealed that Naraku was, in fact, merely another pawn of Magatsuhi's quest to maintain its own existence, which made the Shikon Jewel, or rather Magatsuhi, has been the true enemy of the entire story; Naraku was nothing more than an instrument it created to assure its continued existence. Ironically, it was the master manipulator that was manipulated into fulfilling the actions that generated the entire plot. Naraku's promised reward, Kikyō's heart, was withheld when he finally completed the jewel. In the end, Naraku was casually tossed aside once he had fulfilled his purpose of preserving the jewel.

Physical description
While he is a gestalt; an amalgamation of demons forming an oriental sort of dragon residing in the Shikon Jewel, his incorporeal form is that of a disembodied pale face with red eyes and sclera and blue stripes on his cheeks. When he manifested in the living world through Naraku's flesh, he assumed the form of an adult male with long, shaggy white hair similar to Inuyasha's, smaller facial markings, blue lips and wore a set of dark armor. His arms were of a pale purple colored and most of the time, were a set of three sharp tendrils. As the body did not truly belong to him, he could deconstruct it back into the parts he borrowed from Naraku, keeping only the head in its form so he can speak.

Personality
As the embodiment of the darkness of the Shikon Jewel (and the indirect reason it exists), Magatsuhi is pure evil, perhaps even more so than Naraku himself. He views every other single being, living or not, as inferior to him, repeatedly calling Sesshōmaru weak and disliking any comparisons of him to Naraku. He sneers at courage and self-sacrifice as seen when badly injuring Miroku and Sango, taunting Miroku for absorbing Magatsuhi's deathly poison to save Kohaku from him and sneering that he will die. He is also sadistic, promising Sango he will return her brother as a corpse once he is through with him.

Powers & Abilities

 * Expert Strategist: Magatsu's very cunning where he immediately recognizes any advantage he so has during a battle to further achieve his victory. This is shown when he specifically possessed Kohaku in order to take advantage of Sango's familial ties with him and possessed Inuyasha while he was nearby Rin in order to take advantage of Sesshomaru's connection to her. Finally he had Inuyasha send Kagome falling down to her death so that he may possess her when Inuyasha jumps to rescue her. However Magatsuhi's sadistic arrogance was his undoing as he underestimated the strength of Inuyasha's willpower and demonic powers that led to his destruction by Sesshomaru's Tenseiga.
 * Immense Demonic Power: Representing the evil of the Shikon Jewel, Magatsuhi is extremely powerful, having backed both Inuyasha and Sesshōmaru in demon form into a corner. His power appears to exceed even Naraku's, calling himself a league far beyond his.
 * Immense Corruption: The darkness of Magatsuhi's demonic powers is so vast and dense that a simple stare corrupted and temporarily knocked out Kagome and simultaneously sealed away her spiritual powers. In fact he even managed to corrupt the Shikon Jewel shard within Kohaku's neck with a mere touch while Naraku can't even touch it without risk getting purified by Kikyo's light imbued within it.
 * Shape-Shifting: Magatsuhi has the ability to transform a part or his entire body into a plethora of large, thick tentacles capable of deadly constriction as well as used for impaling enemies. Magatsuhi has no definite form. Like Naraku, he, too, is an amalgamation of demons, briefly borrowing flesh from Naraku to assume a physical form in the material world.
 * Immortality: As Magatsuhi is the demon spirit residing within the Shikon Jewel, he is virtually immune to all forms of physical damage as since the form he was in during his initial battle against Sesshomaru is borrowed flesh from Naraku, he was able to survive a decapitation like nothing. This also extends to his spirit form where being a mere spirit left him unable to be harmed by physical attacks and only Sesshomaru's Tenseiga was able to vanquish him. Even then because he was the evil of the Shikon Jewel, this only sent him back into the jewel, and thus in the manga his spirit was only finally destroyed when Inuyasha cuts with Meidō Zangetsuha the point of light in the darkness inside the jewel, which is the key left by Kikyo before dying to kill Naraku and destroy the jewelry evil. In fact, with Inuyasha's attack at this very point, the purity of the Jewel called Naohi annihilates the evil corrupting presence within it, then the Jewel's shimmering and voice completely stopped. Instead, in the anime version, he is destroyed forever when Kagome wished for the jewel to disappear forever which freed all the spirits trapped within it.
 * Possession: Magatsuhi can possess another's body. He did this to Rin, Inuyasha, Kohaku and narrowly done so to Kagome as well. However his possession is not absolute as his spirit can be drawn out of another's body by a strong enough Yoki such as Inuyasha's Yokai Form's Yoketsu.
 * Demon Bone Possession: During his possession of Kohaku, Magatsuhi was able to possess the demon bones used to create the demon slayer's kusarigama to cause it grow and extend itself to attack at unsuspecting angles.
 * Enhanced Miasma: Magatsuhi's miasma is one of the strongest if not the strongest in the entire series. His miasma is strong enough to seriously injure Sesshōmaru who is very much immune to poison and is of course fatal to humans. His miasma almost killed Miroku who, if not for Magatsuhi fleeing from Sesshōmaru through Miroku, would have certainly died.
 * High-Speed Regeneration: Magatsuhi's true form is able to regenerate within a matter of seconds, or become the several demons that he used to be, as demonstrated when Inuyasha attacks him with the Wind Scar in the final battle to save Kagome.

Trivia

 * His seiyuu as unified consciousness, Takeshi Kusao, also voiced Bankotsu.