Yuki Nagato (長門 有希,
Nagato Yuki) is a
main character in The Melancholy of Haruhi Suzumiya (Suzumiya Haruhi no Yuuutsu).
Yuki Nagato was originally the lone remaining member of the Literature Club, to which all previous members had left the year before. Yuki was apathetically fine with Haruhi taking over the Literary Room for her new club and was soon considered a member of the SOS-Dan herself. In Haruhi's eyes, she fulfills the Silent character type personality.
Yuki Nagato is almost always silent, and will only respond monosyllabically when spoken to, though this is not out of shyness nor seriousness, but simply of there being no need for her to talk the majority of the time. When she does talk, she usually provides a complex explanation using mostly scientific terms to explain even the simplest of things.
Early on, Nagato reveals herself to be a "humanoid interface" or alien android to Kyon. She was sent by the galaxy-wide group of information synthesis thought-entities to investigate the cause of the "explosion of information" 3 years ago which far exceeded anything they have ever observed. When it was determined to be Haruhi Suzumiya, Nagato was set up as an objective observer along with other humanoid interfaces to observe data provided by Haruhi.
As a Humanoid Interface, Yuki reveals herself to be the most actively powerful of the group. Near godlike in her abilities, Yuki can perform 'data manipulation', reprogramming the current data of reality at will. However, she can only reprogram currently existing data, and not create data out of nothingness (she could turn a chair into a sword, but she couldn't create a sword out of nothing). She rarely uses these abilities openly.
Yuki remains passive at the start of the series, only interacting if it is necessary to maintain the status quo of the current situation, as the Information Synthesis Thought Entities have decided to continue observing without Haruhi being effected by external 'paranormal' stimulus. As time goes by however, Yuki becomes more responsive to certain actions and helps out in minor ways. It was also discovered that she has been manipulating events behind the scenes in order to maintain the status quo.
Starting out emotionless, Kyon has come under the suspicion that Yuki is slowly opening up over time, as she displays certain signs of boredom, loneliness, competitive passion and maybe even love. It is unknown how these will effect her current mission, but it has been warned that if the opinions of Yuki's master were ever to change, then Yuki could become an enemy of the SOS-dan.
In the end of the Melancholy of Haruhi Suzumiya arc, in the anime, Yuki promises she will protect Kyon from any Human Interfaces should they attack Kyon like Asakura did. This could mean that even if her master changed views, she still might protect Kyon. She also in this episode says she personally wishes for Kyon and Haruhi to return.
Near the end of the series, Nagato starts to take a full interest in computers. It appears she enjoys using primitive technology, especially when limiting her abilities to the current level of earth technology.
