Yuki Nagato

Yuki Nagato  is a major character from The Melancholy of Haruhi Suzumiya, and the main villain of the second arc of Pretty Soldier Sailor Stellar. Her borrowed Senshi form is Sailor Snow.

Personality
Yuki, being created by the Data Integration Thought Entity, has limited social abilities, which she claims will affect her until she ceases functioning. She rarely speaks, and when she does it's in a monotone voice. Yuki has a poor understanding of emotions, especially her own.

These are traits are not shared by all creations of the Data Integration Thought Entity, and example of which being Ryoko Asakura.

Appearance
Yuki has short lavender purple and brown eyes. She wears the standard North High female uniform at all times, even during summer break.

She used to wear glasses before the incident where Ryoko tried to kill Kyon.

The Melancholy of Haruhi Suzumiya
According to Yuki, she was created three years prior to meeting Kyon and Haruhi, with the purpose of observing humanity and its ability to evolve in intelligence, and more importantly, Haruhi Suzumiya and the data flare that she created around that time. To Yuki, Haruhi is the key to evolution. Yuki is stationed in an apartment complex where several other Humanoid Interfaces are implied to live.

Yuki remains in standby mode until "Bamboo Leaf Rhapsody", when a future version of Mikuru and Kyon come to visit her, telling her that they are from three years later and require her assistance to return to their time. After synchronizing with her future self, Yuki confirms them as acquaintances, and puts them in a room for three years, freezing time within in order to help them return. Meanwhile, another future Mikuru and Kyon come, informing her that in three years the world will be altered and that she needs to help them. Knowing that she is the one responsible for changing the world, she gives Mikuru and Kyon the tools needed to change her astray self back to normal.

Three years later, Yuki attends North High and becomes the only member of the Literature Club. This becomes a selling point for Haruhi, who immediately uses her room with only one occupant. Haruhi eventually comes to use Yuki as a part of the SOS Brigade.

Yuki is the first to tell Kyon about her identity as an alien; Kyon thus trusts her the most out of the three supernatural brigade members. During an early SOS Brigade trip, Kyon took her to the library and got her a card. When Ryoko Asakura tries to kill Kyon in the hopes that it would cause Haruhi to create a data explosion, Yuki saves his life, but forgets to repair her glasses, the first sign that she is fallible. Yuki is also one of the people who gives a clue to Kyon about how to get out of the closed space created by Haruhi: "sleeping beauty".

Yuki stages Emiri Kimidori in the "Mystérique Sign" incident as a pretend client in order to save a bunch of people trapped in an alternate dimension due to a logo Haruhi makes, in order to keep Haruhi entertained. She continually pulls strings from behind the scenes in a similar way Itsuki does.

During the filming for "The Adventures of Mikuru Asahina", Haruhi accidentally causes the Mikuru Beam to become real, and thus Yuki is forced to take a large role in preventing Haruhi noticing by blocking the Mikuru Beam with her hand and injecting nanomachines into Mikuru (biting her) to prevent it from materializing again.

In "The Day of Sagittarius", Yuki is revealed to have somewhat of a passion for computers and hacking, something Kyon does not fail to notice. He supported her participating in occasional Computer Research Society activities over Haruhi's objections. According to the Computer Research Society's president in The Dissociation of Haruhi Suzumiya, she is very helpful and even creates a new OS that everything is compatible with.

The Disappearance of Haruhi Suzumiya
Yuki's most prominent moment is in The Disappearance of Haruhi Suzumiya, in which due to "errors" (which Kyon classifies as "emotions") Yuki steals some of Haruhi's powers to create an alternate universe in which Haruhi, Itsuki, Yuki, and Mikuru are normal humans, Haruhi and Itsuki do not attend North High, Ryoko is a student, and there is no SOS Brigade. Kyon notices a stark difference in her actions up until that point, mainly because Yuki had been anticipating this would happen and was unable to prevent it. In the alternate world, Yuki is simply a shy, introverted girl, but clearly has true emotions because she shows fear when Kyon first bursts into her room. As she still lives alone, this becomes a problem because she rarely gets the will to eat and Ryoko must act as a concerned neighbor and bring her food. Yuki clearly takes an interest in Kyon, as she invites him to the Literature Club and gets him to stay for dinner by pulling on his sleeve. Kyon eventually turns the universe back to normal, after realizing that Yuki preserved his memories of the former world because she trusted his judgment and wanted him to make the choice.

Kyon was sent back to see Nagato three years previously. He and Adult Asahina met at her place, where they discussed the incident. Nagato attempted to synchronize with her future self but failed, but was given a message - it was her that had altered the world in the future. Unable to leave due to the need to keep the "other" Kyon and Asahina "frozen" in time, Nagato gave Kyon a device he would use to inject her human self to transform her back—her glasses, transformed into a "gun". She told them they had to arrive right after the world was transformed. She injected them with protective nanites and programmed Asahina's TPDD. They arrived December 18th and witnessed Nagato changing the world, creating a timequake in the process. Kyon advanced on the human Nagato and, upon realizing she no longer recalled her past, attempted to transform her. Unfortunately, Ryoko Asakura, seeing him as a threat to Nagato, attacked him, stabbing him in the back with a knife.

Another version of Nagato, Asahina and Kyon arrived from the future to rescue the situation, changing human Yuki back to normal. Kyon ended up in a hospital, but with much lighter injuries due to Nagato's reality-altering powers.

Kyon awoke three days later, and went to see Nagato. She told him the Data Integration Thought Entity threatened to delete her for her accumulated "errors" causing her to malfunction; however, Kyon blackmails the Entity into keeping Nagato alive. He came to believe these "errors" were in fact emotions.

Pretty Soldier Sailor Stellar/Sweet Guardian Sailor Cookie
(Note: Yuki arrives in the Mooniverse after the events of the Disappearance arc but before The Rampage of Haruhi Suzumiya)

Human Yuki
This version of Yuki is only shown in the Disappearance of Haruhi Suzumiya. In the new world, Yuki is a shy human girl who loves to read.

Trivia

 * Technically, Yuki is 1,319 years old when one takes into account she spent in Haruhi's time loop during the "Endless Eight" saga.Her short story Editor in Chief★Straight Ahead! suggests that she may be even older. However, Ryoko Asakura referred to her as having a short three years of life.
 * Yuki's English Dub name would be 'Eva'.
 * "Nagato" means "Gate Master" or "Long Gate".
 * According to some fans, Yuki does not like or perhaps even hates Mikuru, seeing her as a potential romantic rival to Kyon. This makes sense, since continuously throughout the anime, Kyon adores Mikuru for her cuteness and appeal, and seems to glare at Kyon after he took Mikuru on a "date" in The Melancholy of Mikuru Asahina. In The Disappearance, alternate Yuki appears to be interested in Kyon, making this theory more valid.