Naraku's incarnations

Naraku's incarnations were created to get rid of unnecessary parts as well as keeping a better eye on Naraku's surrounding situations; Naraku was constantly releasing detachments of himself to carry out his bidding. Only a few of the detachments truly lived up to their purposes as most betrayed him or were quickly disposed of by the people going after him. As of Chapter 548, with the death of Byakuya, Naraku no longer has any detachments:

Kanna
Kanna is an albino girl that barely speaks. She is a demon of mu, "void" or embodiment of nothingness; which also explains why she has no demonic aura. Kanna comes from an old word meaning "godless world." She is Naraku's first detachment, and remains utterly loyal to him while knowing that they are just used as tools in his schemes. Representative of the void in which she controls, Kanna herself is completely devoid of any emotion, never questioning any orders given to her by Naraku. In Chapter 480, after a failed attempt to destroy Inuyasha's Tessaiga, Naraku orders her to commit suicide by shattering herself—as a final attempt to destroy Inuyasha's group (In the anime he destroys her heart). In her final moments, however, Kanna seemed to display some signs of emotions, as if she really did not wish to die. It is in her death that she commits her only act of defiance to Naraku: As a shard of Kanna's shattered body flies into Kagome's eye, Kanna uses this opportunity to show Kagome the light that is present within the Shikon no Tama, which could be the key to defeating Naraku.

Kagura
Kagura is a powerful wind sorceress. She is the first of Naraku's detachments to appear in the manga and the anime, though by order of birth she is actually his second detachment. Naraku endlessly uses her as bait to test his enemies' strength and, aware of her betrayals, keeps good watch over her. Her storyline is constantly followed as she plots to destroy Naraku and win back her heart, often in combination with Sesshōmaru, to whom she is attracted. Eventually, she is killed by Naraku after she openly betrays him to protect Kohaku.

Goshinki
The third detachment of Naraku, Goshinki was a large horned ogre with the ability to read minds. He was extremely agile, physically very powerful, and had teeth so strong they ultimately broke the Tessaiga. That, however, ended up being his own undoing. As happens whenever his sword is taken away from him in life-risking situations, Inuyasha transformed into a full yōkai out of desperation and thus quickly destroyed Goshinki. Following his death, Sesshōmaru contracted Kaijinbō to create Tōkijin from the fangs of Goshinki's head.

Jūrōmaru
He was the fourth detachment and brother of Kagerōmaru, who lived in his stomach. Unlike the other detachments, Jūrōmaru lacked any intelligence, acting simply as a feral beast that could only be controlled by his brother. Indeed, Naraku kept him shackled to maintain some control over him. Both he and Kagerōmaru loved to feast on the insides of those they killed. He and his brother Kagerōmaru were both killed in battle by Inuyasha with his Tessaiga.

Kagerōmaru
He was a small, fast and intelligent detachment from Naraku, proving to be a worthy adversary to the wolf demon Kōga. Unlike most detachments, he was born with his brother at the same time. He was not loyal to Naraku, even trying to kill him by decapitation and had his heart squeezed as punishment before being sealed in his younger brother's gut. Like Jūrōmaru, he loves to feast on the innards of those he fights. Kagerōmaru's appearance bares similarity to a parasite, which takes residence in other people; he further proves this similarity by being able to hide within Jūrōmaru's stomach for sneak attacks. He and his brother Jūrōmaru were both killed in battle by Inuyasha with his Wind Scar.

Un-named Yōkai
An unknown yōkai was created by Naraku in Chapter 174 in the manga, right after Kikyō destroyed Naraku's right arm. Its body structure was similar to Kagerōmaru's. Out all the incarnations Naraku created, this one had the shortest life - only a few moments. It slithered out of one of the pots containing Naraku's flesh and attempted to wrap its tongue around Kikyō's ankle. However, the very moment it does, it disintegrates into ash. Kikyō had armed herself with the dirt from Onigumo's cave, which absorbed the bandit's lust for her; this demon served as a preview of what would happen to Naraku himself if he attempted to harm Kikyō. Given that its brain and ribs where exposed, it is highly possible that this incarnation was not fully completed.

Musō
Musō is the reincarnated Onigumo, Naraku's human kernel. Naraku dumped him in order to get rid of his feelings towards Kikyō, which Naraku felt impeded him from defeating her. Due to Onigumo's disfigurement, Musō was born faceless. He attacked scores of men until finding a face he thought was appropriate for himself. At first, he appears to have no memory, either of his life as a person, or as the human heart of the half-demon Naraku, who shut him off shortly after being born so as to avoid being overcome by Musō's human feelings. Musō recalls his memories during his fights with Inuyasha, remembering also of his attraction to Kikyō. He is ultimately reabsorbed by Naraku after a short time of independence. He demonstrated infuriatingly powerful regenerative abilities, able to piece himself back together even after taking the Wind Scar from Inuyasha. However, had Musō's heart been destroyed, not only his but Naraku's downfalls would have been assured. He also demonstrated the ability to shapeshift new limbs, spikes, multiple legs and arms, claws, and a tail. Unlike Naraku (post-Hakurai-zen) Musō could not regenerate his clothing, forcing him to constantly murder others for new outfits.

The Infant
He is a child with the ability to force other people into doing his bidding by manipulating the corruption within their hearts. He used his powers to track down the whereabouts of a Shikon no Tama shard. During his journey, the Infant was cut in half by a priest's spiritual powers. The left half (which remained as the Infant) was taken by Kanna, whilst the right one (which became Hakudōshi) was put in the charge of Kagura. He later is placed inside the haku (life force) puppet, Mōryōmaru, in a plan to make it so strong that it would be capable of overthrowing Naraku. In Chapter 446, however, Naraku manages to absorb Mōryōmaru, and with it, the Infant. In Chapter 448, Naraku disappears along with the Infant, and by his next appearance in Chapter 452, has reabsorbed him.

Hakudōshi
He is an incarnation that separated from the Infant. Taking the form of a young child, he was able to tame the horse demon Entei. He continues the Infant's quest to get the last Shikon no Tama shard. After Naraku is nearly destroyed at the boundary of the afterlife, Hakudōshi is charged with flushing out Kikyō. Tiring of being under Naraku's thumb, just as the Infant and Kagura were, Hakudōshi created Mōryōmaru to protect his other half; they plotted to replace Naraku and take the Shikon Jewel for themselves. However, Naraku destroyed his barrier and left him without any Saimyōshō, allowing Hakudōshi to be killed by Miroku's Wind Tunnel.

Byakuya
Naraku's ninth and final incarnation that first appeared in Chapter 397, as well as the fourth episode of the Final Act. He was created to replace Kagura, serving the purpose of tracking down Mōryōmaru while keeping tabs on the full-extent of Inuyasha's Tessaiga. Byakuya uses origami as his primary weapon, while also having ability to weave illusions and warp others to different dimensions to avoid interference. Like Hakudōshi, he is linked to Naraku, although on a higher scale; if Naraku loses an arm, Byakuya loses the same limb as well. He was killed when Inuyasha used the Cutting Meidō on him after he attacked Kagome. Unlike his other siblings, Byakuya accepted his death.

Trivia
Naraku's incarnations die in episodes with titles mentioning something related to them:
 * Goshinki died in "Tetsusaiga Breaks"; he broke Tessaiga.
 * Jūrōmaru and Kagerōmaru died in the episode that used their names as it's title.
 * Musō was reabsorbed in "Three-sided Battle to the Death", he was fighting Naraku and Inuyasha.
 * Hakudōshi died in "Naraku's Heart"; he was originally part of the Infant, who houses Naraku's heart.
 * Kagura died in "Kagura's Wind"; she controlled the wind.
 * The Infant was reabsorbed in "The End of Mōryōmaru"; Naraku absorbed Mōryōmaru with the Infant inside it.
 * Kanna died in "Kanna's Gravestone"; her broken mirror was all that was left of her.
 * Byakuya died in "Naraku's Uncertain Wish"; he cut Kagome with a Meidō, helping fulfill the wish the Shikon Jewel forced Naraku to make.