A tragic soul left to endure heartbreak after heartbreak; YS was once a bright and exuberant vocalist before the death of his girlfriend. Even years later, he hasn't recovered, but with the help of his current partner, FLAn - who is equally as odd as YS - he's learning to let go. 
YS is rather literal-minded and sheltered, casting himself out of civilization and hiding away in a remote cave with his partner. He has no desire to return any time soon and is happier with FLAn.