Nue

is a yōkai that was created by Root. It is the result of Project Gozu Tennō, designed to be the ultimate weapon harvested from Hashirama Senju's cells. While spearheaded by Tanuki Shigaraki, it was passed on to his daughter Sumire Shigaraki with the intention to wreak havoc in Konohagakure.

Background
As Danzō continued his amoral methods to protect Konohagakure, realising the potential power within the First Hokage's very cells, he harvested some of them. Placing Tanuki Shigaraki, one of his top researchers and most loyal followers on the project, the goal was to create an ultimate weapon. After Danzō's demise, the blindly loyal Tanuki grew to resent Konohagakure for "betraying" Danzō. Desiring to avenge him, he relentlessly continued his research into finishing the project, all while training his daughter to properly wield the power of the beast in the event he died before its completion. Eventually, he met his own demise after passing the Nue on into Sumire. In the following years as Sumire established a new identity, she began nurturing the creature's development, forming a strong bond with its summoner.

Personality
While seemingly a rampaging beast drawn to people of negative emotions, Nue is in fact extremely loyal to its summoner, Sumire. Despite the dark nature of its creation, it is filled with love towards Sumire, having come to view her as its parent after spending years being nurtured by her. It was even willing to sacrifice itself to ensure her survival. While in its diminutive form, it likes to remain perched on Sumire's shoulder.

Appearance
Normally, it appears as a shapeless dark purple mass. While absorbing enough chakra, Nue takes a tangible form that is reminiscent of a chimera: it is large and has a monkey's head with large fangs and a white mane, a tanuki's body, a tiger's legs, a white snake for a tail and glowing yellow eyes.

After the Gozu Tennō was destroyed, the strong personal connection Nue forged with Sumire allowed its core to be sealed within Sumire's left palm, taking the form of a small red dot that acts as its eye. Later, through a summoning contract, Nue is able to take solid form again, albeit as a chibi version of itself roughly the size of a house pet. Sometime after Sumire became a genin, Nue became able to temporarily further mature its form into roughly the size and shape of a large jungle cat.

Abilities
Nue is able to sense the negative emotions in an individual, using that to select its target. Once it possesses someone, it preys on their emotions, making them give in to their darkest impulse leaving the victims themselves unaware. Only when the victim overcomes their negative emotions or is knocked out will the spectre be forced out from its vessel. It also appears able to feed off their victim's chakra as sustenance, using it to take a physical form to attack independently.

In its fully tangible state, Nue is shown a unique form of regeneration, able to grow several smaller versions of the limb from the stump. It is very strong, able to smash through multiple giant stone walls and highly resilient as launched kunai merely bounce off it. Its endgame ability is to use the collected chakra to self-destruct in a powerful explosion. It is also able to use Space–Time Ninjutsu to teleport, escaping giant barriers. It can also manifest its chakra as tangible constructs. After Nue's form was reduced to a chibi-level, its abilities were also apparently equally reduced in might. Later however, through training from Sumire, Nue is able to transform into a relatively larger form for additional strength.

Academy Entrance Arc
On the night before the Academy entrance ceremony, when Denki Kaminarimon was struggling with his strained relationship with his father and his constant bullying, Nue influenced Denki, until Boruto Uzumaki freed him the next day. Weeks later, when Metal Lee became ashamed at his social-anxiety, Nue influenced him until the next day. When Boruto attempted to perform the Summoning Technique at the Academy, Nue's tail manifested and attacked the academy students until Konohamaru Sarutobi defeated it.

Sometime later, Nue influenced an expelled academy student until Mitsuki defeated and subsequently freed the boy of the influence. The next day, Nue influenced a repairman who was working on the Academy until academy students freed him. During the afternoon, it influenced Shino Aburame, leading to him attempting to kill three of his students the next day until Mitsuki freed him.

Later, when Magire Kakuremino became sadden when Sumire turned down, Nue influenced him for a short time. In the following days, Nue's rampage escalated throughout the village. When Sumire began temporally working at the Konohagakure Water Purification Plant, she had Nue influence a worker, to intentionally get injured, until the Seventh Hokage intervened. Upon realising that Boruto could see Nue influencing Negative Chakra, Sumire strategically had Nue target individuals in area's of the village away from him. Upon influencing Komame, Sumire's classmates confronted her in the act, leading to Sumire escaping and Nue being attacked by Boruto's explosive kunai.

Later, realising that she was found out, Sumire left the hospital to begin the endgame of her plan. She was intercepted by Sai Yamanaka's unit, who initially managed to subdue her. She managed to escape by unleashing Nue, who's tangible form began to unleash a rampage. Kakashi Hatake made the first strike, severing the creature's tail, only for it to grow dozens of smaller tails in its place to steal nearby people's chakra. Kakashi than organised the shinobi to form a barricade to keep the Nue contained. Meanwhile, Boruto, who was confronting Sumire, began to have a strange reaction to the events, causing his right eye to act erratically. This drew the attention of the Nue, which teleported above Boruto. Wanting to complete the Nue's development, Sumire offered herself to the creature, which swallowed her whole before disappearing into a void.

As Boruto and Mitsuki followed through the void into the pocket dimension, they quickly resumed battling Nue. While they were able to restrain it, Sumire quickly came to its defence. Boruto continued to reach out to her, insisting that violence was not what she wanted unlike her father. Desperately clinging to her father's request, she ordered Nue to take her chakra and finish the plan. Nue instead ignored Sumire's order and instead snuggled against her. While Sumire was confused by this event, Boruto deduced that having been nurtured by Sumire all these years, it came to view her as its parent. Insisting that Sumire doesn't want it to hurt people any more than she does herself, Sumire finally let go of her anger. This caused the Gozu Tennō to be destroyed and the dimension to begin crumbling around them. Nue then aided its surrogate parent and her classmates into escaping the dimension, causing it to be left behind from falling debris. Despite this, the strong connection it developed with Sumire allowed her to retain a piece of its essence, letting Nue live on sealed in Sumire's left palm.

Graduation Exams Arc
When Sumire and her friends went camping to capture a famed Eternal Carp, Sumire summoned Nue. The miniaturised creature quickly jumped on Sumire's shoulder and aided its master, using its chakra to strengthen Boruto's fishing pole.

During the practical test of the graduation exams, as Sumire battled against Konohamaru, she summoned Nue to attack him. After a short scuffle, he repelled the creature with his Lightning Release. Later, Nue helped free the captured students from the teachers by sneaking in while the Sumire and her allies distracted them.

Versus Momoshiki Arc
During the first round of the Chūnn Exam, a trick question was used that sent all participants plunging into a pit. Sumire summoned Nue to save the team with its chakra.

Some time later, Nue was summoned to help Namida Suzumeno grow stronger and develop a new technique. The tiny summoning charged around acting as a target for Namida to strike and dodge. Later, the training apparently helped Nue as during a mission to protect sacred antiques, Nue morphed into a larger form, easily subduing a foe and getting praise from Sumire.

Jūgo Arc
In the anime, when Team 15 was assigned to work with Team 7 on the mysterious attacking of wildlife on a village, Boruto was attacked by Jūgo in his savage Sage Transformation. Nue was summoned to aid Boruto, knocking the man off the cliff an into the river. Later, when the villagers found an unconscious Jūgo in his normal state, Nue quickly showed its distrust of the man, but was held back Sumire.

Later, after Tosaka concluded from a blood test that the outbreak and Jūgo's cursed seal were not related, Konohamaru instructed Team 15 to go back to Konoha to report on it and request backup. On their way, they were attacked by Momo and Sasami, who took the opportunity to test their device based cursed seals. As the empowered foes quickly defeated the genin and infected Namida and Wasabi with cursed seals, Nue fought off the attackers and carried Sumire. It then stood guard on her until she awoke.

Trivia

 * A Nue is a mythological Japanese creature said to have the face of a monkey, the legs of a tiger, the body of a tanuki and the front half of a snake for a tail.