Heh... I got asked that same question on Formspring too.
I guess I'll just restate what I said there. Yureina is a username that goes back to 2008 for me, starting out as the name of my Human Holy Priestess in WoW. When that character proceeded to completely take over my interests in that game, replacing a Scarab Lord Warrior no less, I adapted as my username, since it was my primary WoW character. As time passed, and especially when I build my Goldmaking industry, the name itself began to make a reputation of its own, becoming synonymous with mass wealth, standing up against would-be tyrants, and exceeding all expectations. The humble priestess was able to run wild for over a year at the center of events until I decided to quit, largely due to the personal costs of such efforts.
I quit WoW just over a year ago, and then for good in November, but the name has stuck. You could say that, because of the past reputation I got with the name, I have a sense of pride in those past accomplishments. My keeping of the name is half "tradition" (I have a good name, why not just keep it?), and half a statement I am trying to make. It is a recognition of past deeds (most good, some not), as well as an implicit statement that I seek similar success in the future. "Rei's Story" is far from over. :3
Okee.... I'll stop now. >_>