I think the founder of Songrim placed the ice stone inside the body of the blind girl who we have seen dancing from the beginning of episode 7. Since it was placed inside that girl’s body many years ago, the ice stone will then be passed on to the next first-born of the Jin family since I believe that the ice stone is inside Mudeok’s body whom I also believe to be Jin Buyeon, the long lost-daughter of Jin Hogyeong and eldest sister of Jin Choyeon. To back this up, Mudeok was able to open jinyowon which would not be possible if she didn’t come from the Jin family.

I think the Queen learned about the ice stone being inside Buyeon’s body and was the mastermind behind her disappearance. She stole the ice stone, but only managed to get half of it, dividing the ice stone into two. Thinking that she was able to get the whole ice stone, she killed Buyeon and the latter’s soul eventually perished. The only thing that’s keeping her body alive was the half of the ice stone that is inside her body, acting as the special soul. This is the reason why Mudeok’s body has become weak.

The part of the ice stone that is with Mudeok is the one that can prevent soul shifters from getting wild. We all know that Naksu hasn’t mastered Hwansu yet, and that’s the reason why she did not turn wild when she shifted into Mudeok’s body. Since Mudeok’s body is weak, it needs a powerful soul who can put the power of the ice stone to good use. I believe it was the ice stone that chose Naksu to be shifted into Mudeok’s body. I think the ice stone needs to be discovered to be in that body for the shifted soul to be able to use it in a good way. I think this is also why Naksu can’t use her power, because it’s the ice stone that’s preventing her from using her power for evil.

Then, the other half of the ice stone is with the Queen and uses it in creating soul ejectors. The reason as to why she stole the ice stone because Jinmu told her about what happened between the late King and Jang gang. I think Jinmu and the Queen have an agreement that the Queen will continue to supply him soul ejectors in exchange of the original constellation plate that can prove that Jang uk was born with a King’s star.

For me, Jang Uk’s real father is still Jang gang because when the alchemy of souls between the late King and Jang gang took place, Dohwa was already pregnant with Uk. There was a King’s star when he was born because he was destined to end the alchemy of souls that has occurred between the late King and Jang Gang.