I was able to get the skin by doing the Beastmaster rank 3 requirement, but then it's an automatic gameover. I'm fine with that, however, unlocking the skin to only get a game over is a bit strange. 

If you don't want to use cheat mode (where you can get bad ends and still keep playing) to unlock the skin you can edit your save by searching for "jobClass" and changing it to "QUEEN". Those are the 2 ways I can think of at the top of my head to unlock the skin.