Original character by artist Ken (koala). She appears to have been created for an RPG they were playing, but has since become highly popular, and one of this artist's most iconic characters.
While the smaller details of her design are often changed each time she is drawn, there are several constants: long to very long white hair with sidelocks and a hime cut, some sort of strange headgear, blue eyes (sometimes depicted by fan artists as green), a form-hugging black (formerly blue) bodysuit, and a sleeveless blue microdress with neon trim.