Onigumo

was a bandit rescued by the priestess named Kikyo. He was an evil human being who gained his injuries in a fire caused by Rasetsu who set the building Onigumo was in a blaze because Onigumo betrayed him and took his men. Kikyo found him and nursed his injuries, and, occasionally, Kikyo's younger sister Kaede took care of him as well, even though she didn't like doing it. Onigumo gave up his body to demons in order to regain his strength, mobility, and power. He did this because he desired Kikyo and the Sacred Jewel for himelf, while the demons did it because they wished to get rid of Kikyo and obtain the Sacred Jewel. This created the evil half-demon Naraku who then immediately tricked Inuyasha and Kikyo into becoming enemies so he could have the sacred jewel for even more power than he already had. His deceit led to Kikyo's death and Inuyasha's sealing to the Tree of Ages. When Naraku removed his human heart, he also removed Onigumo's soul in the process, which became Muso. Much later, Muso finally remembers about his past as a bandit and of his time with Kikyo within the cave.

Musō Arc
Musō was separated from Naraku in an attempt to remove his human core, Onigumo, and thus also Onigumo's love for Kikyo.

He was the sixth detachment of Naraku. Naraku cared so little for this incarnation that he gives it no name or face; Muso takes both of those for himself from a wandering monk that he kills. Muso ventures to Kikyo's former village, where he runs into InuYasha's group and battles them quickly after their encounter. Soon Naraku quickly realizes, however, that he cannot abandon Onigumo when demons try to gain their freedom from his body, and Muso is absorbed back into Naraku.

Muso had the form of a faceless man with a spider scar on his back. He is faceless because Onigumo was badly burnt before becoming Naraku, even his face was burnt off. Therefore Muso recieves the same outcome. He goes around killing many people to take their face, eventually ending up with the face of the monk Muso (which is where his name came from). When he comes across InuYasha and the gang, he seems to be immune to their attacks and is even able to regenerate himself after being torn to pieces by the Tessaiga.

Soon after, Naraku re-absorbs Muso since he feels that he has not gotten completely rid of Onigumo and possibly the threat of his death. He decides to try again later when he is stronger.

Meeting Naraku
The poisonous insects take Muso to nearby forest where Naraku is waiting. For the first time ever Naraku and Onigumo come face to face with each other. In the manga Muso instantly attacks Naraku and is absorbed almost immediately. The anime goes into further detail with the encounter. Naraku tells Muso that Kikyo is alive again and she is as he remembers her. Before he can question Naraku about Kikyo InuYasha and Miroku appear. As InuYasha starts a fight with Naraku, Muso runs away. Still angry at Naraku for his imprisonment he decides to go back to kill Naraku. He stabs Naraku in chest however doing this allows Naraku to reabsorb him. Naraku reveals that he still needed Onigumo's heart as a connector for his body, which why he needed to reabsorb him.

Abilities

 * Facial theft - Having been created without a face, Muso can take on facial identities of others by apply faces to his head after ripping them off.


 * Regeneration - Muso demonstrated infuriatingly powerful regenerative abilities, able to piece himself back together even after taking the Wind Scar from Inuyasha. However, had his heart been destroyed, not only his but Naraku's downfalls would have been assured. He also demonstrated the ability to regenerate and shapeshift new limbs, spikes, multiple legs and arms, claws, and a tail.

Reuniting with Naraku
Realizing he was not yet ready to part with Onigumo's soul, Naraku confronted Muso and tried to absorb him back into his body. Inuyasha interfered, enabling Muso to run, but he foolishly went back to kill Naraku for revenge. Muso impaled Naraku but Naraku drew him in and absorbed him as he screamed for Kikyo, Kagura looking on as she thought, "If I'm not careful, that will be my ultimate fate..."

Final Death
In one of Naraku's final moments he recalled that Kagome said the the Jewel did not grant his real wish. Naraku recalls that what he really wished for was Kikyo's love, but it seemed that it was not granted to him. Before Kagome's arrow pierced the jewel, Naraku comments that he won't be able to go where Kikyo has gone. It is presumed that Onigumo's emotions have somehow surfaced within Naraku as he recalled his true wish.

Trivia

 * Even though Naraku was the ruling personality of Onigumo's former body, Naraku seemed to retained some of Onigumo's memories, and desires as well: The Shikon Jewel, and the Priestess Kikyo.
 * Fans thought that Naraku was Onigumo but some thought that Naraku was a third personallity with his own Soul (one is Onigumo, one are the demons which 'create' Naraku as well).
 * Onigumo had a Spider mark on his back, even before he became Naraku.

Name Meaning

 * The name Onigumo literally translates to Ogre/Demon Spider, most likely referring to his demonic spider mark on his back, and possibly Naraku's spider-like traits.According to Japanese History, Japanese people used "Tsuchigumo" (ground spider) as a derogatory term for bandits and thieves
 * The name Muso in which he used to call himself when he stole the face from a monk whose name was Muso. Translated Muso means Peerless.