
I think he's a representation of all the stress and trouble slowly getting to him. He survived so much trauma yet never had the time to rest and heal.
I also think he's unconsciously scared of what will happen if he let all the power get to Wolgang's head; Shin knows what he's capable of doing and always have made his moves based on others' well being, so I think the other Shin is the part in him that wants to be selfish.
As I said, he's dealing with a lot of mental and physical issues and perhaps the other Shin can be showing how he's getting close to his breaking point. (Probably mentally)
We have to wait and see but I don't think it's a case of another personality, I think it's Shin's inner thoughts and how he deals with himself.
It's also worth noting he was raised under the late king, he knows more than anyone how he can use his talents in another way if he desired to.
In the end, I think it's a show of how scared and unsure Shin is of himself.

I'd say Rafael is the killer because he's obsessive and the prince is the father, based on the crying dragon metaphor it seems unlikely for anyone else to be the baby daddy (The dragon's eye color, etc.)
But the prince could also be the killer since he said how his white rabbit would only stay with him until the case is over, and how he ignored Louise for 4 months so that he'd come to him; it'd also make for heavy angst and a good story
But I don't think that'd be the case
Damn I want a gf