Onigumo

was a bandit rescued by the priestess named Kikyō. 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. Kikyō found him and nursed his injuries, and, occasionally, Kikyō'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 Kikyō and the Sacred Jewel for himself, while the demons did it because they wished to get rid of Kikyō and obtain the Sacred Jewel. This created the evil half-demon Naraku who then immediately tricked Inuyasha and Kikyō into becoming enemies so he could have the sacred jewel for even more power than he already had. His deceit led to Kikyō'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 Musō. Much later, Musō finally remembers about his past as a bandit and of his time with Kikyō within the cave.

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

He was the seventh detachment of Naraku. Naraku cared so little for this incarnation that he gives it no name or face; Musō takes both of those for himself from a wandering monk that he kills. Musō ventures to Kikyō'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 Musō is absorbed back into Naraku.

Musō 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 Musō receives the same outcome. He goes around killing many people to take their face, eventually ending up with the face of the monk Musō (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 Musō since he feels that he has not gotten completely rid of Onigumo; possibly the threat of his death. He decides to try again later when he is stronger.

Meeting Naraku
The poisonous insects take Musō 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 Musō instantly attacks Naraku and is absorbed almost immediately. The anime goes into further detail with the encounter. Naraku tells Musō that Kikyō is alive again and she is as he remembers her. Before he can question Naraku about Kikyō, Inuyasha and Miroku appear. As Inuyasha starts a fight with Naraku, Musō 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 revealed that he still needed Onigumo's heart as a connector for his body, which was why he needed to reabsorb him.

Reuniting with Naraku
Realizing he was not yet ready to part with Onigumo's soul, Naraku confronted Musō and tried to absorb him back into his body. Inuyasha interfered, enabling Musō to run, but he foolishly went back to kill Naraku for revenge. Musō impaled Naraku but Naraku drew him in and absorbed him as he screamed for Kikyō, 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 Jewel did not grant his real wish. Naraku recalls that what he really wished for was Kikyō'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 Kikyō has gone. It is presumed that Onigumo's emotions had somehow surfaced within Naraku as he recalled his true wish, thus proving what Kikyo once stated to Naraku was indeed true;"You've disguised yourself well, but you're still that fugitive human, and who you once were can never be erased".

Abilities

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


 * Regeneration - Musō 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.

Trivia

 * 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 Musō in which he used to call himself when he stole the face from a monk whose name was Musō. Translated Musō means Peerless.