Totally fictional. It's the unreal game's username/handle coined by the protagonist of a light novel. From the eyes of a native Japanese, I can't reject such cases that there can be a few of the holders of the same name in sixty million Japanese men. However, it must be just nothing but coincidental. This site is for the sake of concerning the individual names of real people. Please don't confuse that it's like a compilation catalog of imaginary characters. Contaminating with mere fantasies is a kind of abuse. I'd make a proposition of deletion of this topic, if possible.
This is my personal interpretations of the name: In order to see through the meaning one needs to know Japanese, Turkish and Swahili though. Kirito: Kir means “dirt” in Turkish, and “ito” has meanings like “string, connection, wire” etc in Japanese. So maybe Dirty string/connection. Opposite of kir iz temiz (Turkish), temizito; te mizito (mizito means calloused in Swahili) thus temizito means hardhand, thus Kirito means softhand :p it also means noble as nobility do not work using their hands, normally calloused hands are sign of swordsmanship, but he is a cyber swordsman after all. This interpretation is viable when used with suffix kun, Kiritokun, means it’s dirt/dirtiness belongs to full(not hungry). Japanese artists and writers are quite fond of puns. You can see that they derive their inspiration from mythos, history and other artworks in almost every piece of anime.Might sound ridiculous at first i know but who knows... There was this detergent commercial in Turkey of a brand named “Omo” their motto was “Omo beyazlığı” when you translate it to Japanese it means Omo shiroi, and yes Japans were major shareholders of the firm. So what i mean is names might have much more complicated sources/roots even in artwork.
Takes about 30 seconds to look it up. Kazuto Kirigaya -the person who holds the alias Kirito, made the name by combining his first and last names, while playing The Sword Art Online [Closed Beta]