Permission you say?
Personality:
Keep in mind Yuki is like a ghost to the world. Yuki's expression is cold, almost to a deadpan expression although prefers body language than speaking. When needing to speak, she does so in a very concise manner, always speaking in a monotone. She thinks very rationally at times only to do what is necessary to aid the SOS Brigade club and ensure Haruhi doesn't use her godlike powers. Yuki doesn't like people, but she doesn't dislike them on the whole. The person she trusts with things is Kyon, who she has developed the ghost of proper feelings for.
A side from that Yuki enjoys reading; especially science fiction or mysteries. Later in the series, she actually displays her enjoyment of computer games with the Computer Club. She also displays a sense of humor, although with her expression at times you wonder if she is joking or talking seriously. Other than that, Yuki is reliable and trustworthy. She does display caring rarely in the club. One example is by taking care of Mikuri when she fainted on the Murder Island episode.
History:
Yuki Nagato is a quiet high school freshman and former of the Literature Club. All were seniors in the club except for Yuki. When the seniors graduated, the club was left to Yuki and possibly later was disbanded when she joins the SOS Brigade. She is the only member of the SOS Brigade who was not forced into joining by Haruhi Suzumiya. Out of school, Yuki lives alone in an apartment.
What Yuki is really is a 'humanoid interface', artificial human, created by the Integrated Data Entity three years ago for the purposes of interacting with an observing events on Earth. In other words, she is an alien created to observe Haruhi. Haruhi respresents the potential of an evlution in autonomy, that the Inegrated Data Entity does not have.
Yuki possesses numerous abilities as an artificial human. She is capable of manipulating the properties of the environment and any materials within it at any scale to her desire. One example is shown is when she modify a baseball bat to hit only home runs. Another she can do is make a cover up story for Ryoko Asakura moved to Canada (although in reality she kind of deleted her due to her assault towards Kyon). She also can reconstruct a classroom, down to the last detail after everything was completely destroyed. Finally, she is beyond human strength, agility, and stamina. She is able to reconstruct herself after taking multiple damages and can take pain without even phasing (like the multiple of spikes lunging towards her--nothing to her). To sum it up, she is Mr. Smith from the Matrix. The only problem with Yuki is she lacks of understand towards social norms and earth technology, like when she tried to use the mouse for the computer. Other than that, Yuki is indeed Mr. Smith.
Permission:
Ability - Yuki can control data around and in her. She can alter or construct the scenery to whatever she sees fit. She can also enhance her speed and strength to fight if she has to. If you need to cool off she won't hesitate to throw you to the next lake or swimming pool near by like a catapult.
Hacker - Yuki has learned her advantage with computers. In the series, she hacked six times than a regular hacker. Just like reality, she can hack to computers and alter anyway needs of necessary.