No one knows really where synths come from. They sort of just appear, for lack of a better term. But never in large numbers. Enough to be a minority group in the holographic world of lights and concrete. One day, out of the blue, there will be a new tin can walking the streets; no name, child like understanding, and features they need to learn. Some develop quickly into general working class citizens and take on an identity of their own making. Some, however, find they have skills for rather... unsavory occupations.
3K may not look much but that's supposed to be the point. Self named for their sniping distance, they do work as a hitman or bodyguard, although 3K does enjoy being a rooftop runner from time to time. That being said, 3K's loud mouth sometimes gets them into trouble with other people, "fleshbags" mostly. Not that they cares.

Although 3K is nb, there are times where they are fine with being identified as male, given the habits some humans have. They don't care much for sexual acts, nor do they have any interest in exploring or partaking. That being said, they have had their ass touched more than once and jumped by a curious robophile; to their disappointment, 3K is rather flat and bare.
And yes, they did in fact name their sniper rifle Snickers