Onigumo

was a bandit who was rescued by the priestess named Kikyō. He fed his body to yōkai and ultimately became Naraku.

Origins
Onigumo was an evil bandit who met and betrayed Rasetsu by telling him to go after Kikyō who he didn't reveal was being protected by Inuyasha. Thinking the half-demon killed Rasetsu, he made off with the bandit army who accepted him as their new leader. However, Rasetsu survived but lost his eye and tracked down the bandits to an inn. Rasetsu confronted the surprised Onigumo and set the building that he was in ablaze. Rasetsu found that Onigumo had barely survived but gained severe injuries in the fire. To complete his revenge, Rasetsu then had his men throw Onigumo off a cliff to finish him while mockingly telling him to find the shard and greet Kikyō. However, Onigumo managed to survive but was crippled by the fall.

This set the events of the series in motion, as Kikyō later found him, nursed his injuries in a cave, and occasionally, Kikyō's younger sister, Kaede took care of him as well, even though she didn't like doing it. Onigumo originally had difficulties accepting Kikyō's kindness, and told her to forget about the bandit when she visited him, but Kikyō's kindness had also made Onigumo fall for her. Onigumo gave up his body to demons in order to regain his strength, mobility, and power. Onigumo did that 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. That 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.

Reborn
When Naraku removed his human heart, he also removed Onigumo's soul in the process, which became Musō. Much later, Musō finally remembered about his past as a bandit and of his time with Kikyō within the cave. Musō was eventually absorbed by Naraku and became part of him again. When Naraku returned to Mount Hakurei where Onigumo's voice of his heart is, in which that he thinks that Onigumo was right before from 50 years ago.

Final death
In one of Naraku's final moments, after Inuyasha destroyed his body forever with Meidō Zangetsuha, leaving only his soul due to the corrupted jewel, he recalled that Kagome had said the Jewel did not grant his real wish. Naraku's soul recalled that what he really wished for was Kikyō's love, but it seemed that it was not granted to him. Before Kagome's arrow had pierced the jewel, Naraku's soul commented that he wouldn't be able to go where Kikyō had gone. It was presumed that Onigumo's emotions had somehow surfaced within Naraku as he recalled his true wish, thus proving what Kikyō had 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".

Naraku's soul was sealed inside the Shikon Jewel after his purification from the material world. In the manga, although it is not directly explained, Naraku's soul was destroyed forever by Inuyasha when he cut the point of light in the darkness inside the Shikon Jewel with Meidō Zangetsuha, which was very clearly the key to kill Naraku and destroy the jewel of evil. In fact, with Inuyasha's attack at that very point, the purity of the Jewel called Naohi annihilated the evil corrupting presence within it, then the Jewel's shimmering and voice completely stopped.

Instead, in the anime version, when Kagome wished for the Jewel to be destroyed, Naraku's soul was purified and went on to the afterlife. The Onigumo part of his soul seemed dominant at that point, and was finally at peace, where the demon half of Naraku's soul presumably separated from Onigumo and went to Hell.

Physical description
Onigumo's most notable feature was a spider mark on his back, even before he became Naraku. The origin of this strange mark is never revealed.

When Onigumo first appears in Kaede's memories, he appears as a pitiful figure; a crippled man covered in disfiguring burn scars and wrapped head to toe in bloody bandages. His nose was burnt off, as well as his lip in the manga. Onigumo's face was masked in wrappings with the only openings being for his mouth and one remaining eye which was bloodshot from his failing health; the veins around Onigumo's green iris almost resembling a dark spider web.

Before his burns, Onigumo was a young man, presumably somewhere from 17 to 20s, with a toned body and long dark black hair. His face is always out of view in the series and his Musō incarnation had no face, due to him forgetting his face and identity. The manifestation of Onigumo's soul appears in Chapter 452 wearing the same face as Naraku, but it is unclear if this is his true face.

Personality
During his life, Onigumo was a bitter and misanthropic individual; being both nihilistic and hedonistic. Onigumo committed many terrible crimes throughout the land and betrayed his comrades without remorse. Onigumo freely defined himself as a wretched villain with a dark heart.

Onigumo's incarnation as Musō stated the only thing that mattered in life were wealth, alcohol and sex. Musō said he enjoyed massacring villagers and that he'll kill anyone he feels like.

After becoming crippled and burned, Onigumo became depressed, he was hostile to Kikyō and tried to dissuade her from keeping him alive. However he came to be obsessed with her and desired her affection above all else, so much that he eagerly sold his soul to yōkai for a chance to get her.

Relationships
At first, Onigumo was openly open hostile to Kikyō and frequently told her to stop taking care of him, however gradually Onigumo's feelings became more complex and he secretly came to look forward to her visits, however he was also bitter that she would never return his feelings. This anger increased when Onigumo found out that Kikyō loved Inuyasha learned by the Small Spider Demon.
 * Kikyō

During a conversation with Kaede, Onigumo claimed Kikyō was too pure and proud, stating he wanted to see Kikyō corrupted with evil just like the Shikon Jewel. When Musō regained his memories, he said Kikyō was arrogant and self righteous, then followed by how he wanted her.

Musō was despondent that Kikyō had been killed by the yōkai in Naraku, stating that Kikyō alone gave meaning to his life and that there were no reason for living if she was gone. When he found out from Naraku that Kikyō was alive, he was overjoyed and attempted to seek her out, yelling Kikyō's name until he was fully absorbed by Naraku.

At Naraku's death, it is revealed Onigumo's heart wished for Kikyō's love on the Shikon Jewel.

Onigumo knew Inuyasha was protective of Kikyō. He originally wanted the Dog hanyō to kill his former bandit leader Rasetsu but this failed. After being crippled, he became madly jealous of Inuyasha's relationship with Kikyō, as he wanted the Miko's attention for himself. When Musō, the memory deprived incarnation of Onigumo, met Inuyasha, he instantly felt a great hatred within him after looking at the face of the Dog hanyō and tried to kill him.
 * Inuyasha

After regaining his memories, Musō stated Inuyasha should've died instead of Kikyō and he aims to rectify that mistake right now.

Onigumo had a consistently hostile relationship with Kaede; never calling her by name and threatening to corrupt the Jewel and her sister Kikyō. When he met her 50 years later as Musō, Onigumo didn't recognize her and tried to steal her life, saying he had no interest in old women.
 * Kaede

At some point, Onigumo met Rasetsu, a bandit leader and told him about the jewel. However this was a set up as Onigumo told him to go alone, planning for Inuyasha to kill Rasetsu allowing Onigumo to take Rasetsu's gang for his own. After Rasetsu's presumed death, with no remorse, Onigumo celebrated his leadership position by partying at an Inn.
 * Rasetsu

The surviving Rasetsu took back his men, burnt Onigumo alive with the inn and, when finding out the traitor was still alive, tied him up and tossed Onigumo off a cliff by Kikyō's shrine while telling Onigumo to get the jewel himself.

As an elderly man, Rasetsu, now going by the name of Kansuke, said even his younger self couldn't compare to Onigumo when it came to evil. He believed the jewel shard bringing Naraku's demons after him was Onigumo, somehow haunting him even after his supposed death.

Trivia

 * Onigumo (鬼蜘蛛) can also be translated as the Araneus ventricosus, a particular species of orb-weaving spider.
 * It was Naraku's actions that brought some sense of irony with Onigumo's words of how he would have liked to see Kikyō "apprehensive and frightened," a facial expression that was made as Naraku struck down Kikyō, as he was disguised as Inuyasha, though Musō, Onigumo's later reincarnated form, expressed a large amount of anger and regret as he recalled that bitter memory as Kikyō had died from such a mortal wound due to Naraku's miscalculation.
 * As Musō, while Onigumo did remember about the Shikon Jewel, he apparently did not seem to desire the jewel as much as he did with Kikyō, which implied that Onigumo saw the Shikon Jewel as merely a bonus and his main objective was Kikyō.

Media appearances
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Manga

 * Chapter 65
 * Chapter 66
 * Chapter 71
 * Chapter 72
 * Chapter 78
 * Chapter 94
 * Chapter 121
 * Chapter 171
 * Chapter 172
 * Chapter 174
 * Chapter 209
 * Chapter 210
 * Chapter 211
 * Chapter 281
 * Chapter 308
 * Chapter 377
 * Chapter 452
 * Chapter 530

Anime
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 * Episode 20
 * Episode 21
 * Episode 23
 * Episode 24
 * Episode 33
 * Episode 40
 * Episode 41
 * Episode 47
 * Episode 70
 * Episode 71
 * Episode 87
 * Episode 88
 * Episode 124
 * Episode 148
 * Episode 150
 * Episode 169
 * Episode 174
 * Episode 188
 * Episode 192
 * Episode 1 (Hanyō no Yashahime)