Dark-san is actually a shortened form of my previous nickname, Darkyouth. I took that nick off some Counterstrike bot some nine years ago. *Hurray for unoriginality!* I continued using that nick for the next two years in a Pokemon board before deciding that it is time for a image revamp. The revamp was to coincide with my addiction into the Japanese culture.
Back then, most people would referred me as Dark. I stood by that nickname and came out with Dark-san, as a simplest form without deviating from my previous nick of Darkyouth. The revamp worked, people noticed me and I was subsequently promoted to the OA (Other Anime) moderator there. I continued to lurk in the forum for the next seven years till now with that nick.
Even as I registered in MH, I still retain that nick for the sake of easy identification. ^.^; Not a need to go through the hassle of thinking up another nickname.