PhantomzK

To me it was a given that Bu Yeon captured Naksu's soul into her own body. It was previously mentioned that the Jin family are users of 'divine' power with the ability to manipulate and control souls no one else could. I think this is essentially a completely different source of power from sorcery which is akin to black magic and 'magic' itself. As to why Bu Yeon captured Naksu's soul, I think its probably because she is able to see energy and noticed Naksu trying to perform Alchemy of Souls with an innocent person. She probably also saw that Naksu's 'soul' was not 'evil' or maybe she even has some sort of clairvoyant powers we do not yet know of. Thus, she chose to capture Naksu's soul into her own to save the innocent woman.

I think the will of Master Seo Gyeong will play a very important role later on. The purpose of the ice stone was to bring his lover, the Jin founder back to life or something I believe. I think that is why Bu Yeon was born with the same powers as the Jin founder through the ice stone. In a way, his will succeeded through the ice stone after all. She is the reincarnation of the Jin founder. Which begs the question, is Jang Uk the reincarnation of Seo Gyeong? Imo, probably not. His will never mentioned about them being together to the end. It was more wanting to help his dying lover who could not live a good life due to her sickly body or something of the sort. Thats why he left the ice stone to the Jin's, hoping that it can one day bring her back and probably live a more fulfilling life. Thus, I think it might be possible in the end that Bu Yeon will end up dying and their souls will be reunited again in the afterlife. Her true lover is Seo Gyeong, not Jang Uk.

PS, there is one point that I am unsure about however that makes me suspect that Jang Uk might be the reincarnation of Seo Gyeong after all. That is that Bu Yeon's soul seemed to recognize him and has some affection towards him for some reason shown during his soul shifting encounter in previous episodes.

I agree. I don't think that she dies. I think people are assuming that she does because her soul takes over for a bit the moment that Madam Jin attempts to kill her and Mu Deok starts crying. However, she calls her mother at the end of the episode which you clearly see Madam Jin hesitating after that. Thus, it is unlikely that she goes along with killing Mu Deok. Throughout the episode it is clear that she already knows or suspects that So-I is not Bu Yeon and she also seems to have a small inkling about Mu Deok being Bu Yeon. Thus due to Mu Deok calling her mother I think she will hesitate and then not go ahead with it.
Though I don't think that she completely believes that Mu Deok is Bu Yeon yet. However, she probably suspects it at this point, however minor that suspicion is. This case will probably at most solidify her suspicions a bit more. And as you know, she will do whatever it takes to find Bu Yeon. So even if its just a suspicion she will not let Mu Deok die, much less kill her herself.

Or maybe he will try to protect her as much as he can until he reaches Hwansu if this is the case. Or maybe his place has other secrets we do not yet know that can help.

One thing to note is that Songrim bans sorcery entirely if I remember correctly. But outside of Songrim I think some sorcery is still used. They really just hunt down those who use sorcery for malicious intentions I think. Otherwise those small time shamans would long have been hunted down. The only one that they hunted down as far as we know was shaman Choi because she was using it ofr malicious means.

Not Uk. Probably Seo Yul. He seems to have some sort of plan related to Mu Deok/Naksu which may come to fruition in Part 2 which I think will likely take place at his place.

Since we are reaching the end with only 4 episodes left and the enemies are being dragged out into the open, I will assume that Jang Uk's and Mu Deok's main storyline will likely conclude in Part 1. However, we know that Seo Yul is soon to return to his own place and he plans to take something with him which is definitely related to Naksu if not her herself. I previously theorized thay Naksu's original body may not actually have burned (Probably had a switcheroo by Yul or something) or the body can still be recovered in some way. This would be plausible since we have seen Soul Shifter bodies recover through the ice stone. In any case, I think it could be likely that in Part 2, the story will take place in Seo Yul's home and the main storyline may be around him and Naksu played by Go Yoonjung.

Since we are unsure if Jung So Min is returning or not officially, it may be possible that either Bu Yeon officially dies at the end (which I doubt) or its simply that Bu Yeon stays behind at Jinyiwon and Jang Uk goes with Seo Yul to his place with Naksu. If this is the case, then the storyline might still surround Jang Uk and Naksu with Seo Yul just helping.

I have a minor suspicion that the person Seo Yul claimed to be taking with him back home is Naksu's original body. I suspect that the body was not actually destroyed and maybe a switcheroo happened somehow one way or another. Its a world of magic so its not completely unimaginable. Seo Yul probably had something to do with said switch. Otherwise it wouldn't really make sense how the main female lead will once again be Naksu in her own body next season. Of course nothing on this has officially been confirmed yet as far as I know, but I do think this is most likely the case.

So I am gonna go ahead and say that there were actually 3 siblings, 2 girls and a boy. Meaning Triplets. Perhaps the scientists made a minor mistake and missed 1, thus saying that there were a boy and a girl. Of course it could just as well be that they made a mistake with 1 of their genders.

Well its also possible that Naksu was also born from the Alchemy of Souls. We don't actually know when her father had his soul shifted. Perhaps she was born from the soul shifter and then something happened between him and the villian faction which led to him being abandoned by them. I would think its possible that he developed a real connection with his family or at least his daughter which may have played a role in getting abandoned by his ppl. Which could explain why he went berserk.

Of course this is all just a possibility. Wont know until anything is actually confirmed.

Could go 3 ways. 1 where the 2 souls reach some sort of agreement and attain a state of equilibrium in which both souls coexist continually. 2. Naksu either gets overpowered by Mu Deok's soul or gets her soul taken out. 3. Mu Deok not only absorbs Naksu's energy but also her entirety of person, memories, and feelings essentially becoming 1 person. Though in this case it would technically be Mu Deok and the real Naksu would realistically be dead. Part of Naksu would from then on live on through Mu Deok. We know that in the world of Alchemy of Souls, there isnt only genetic inheritance but also soul inheritance as shown by how Jang Uk has the Kings star due to his soul descending from the previous king. He is destined to be king despite not biologically descending from the king. His soul inherited the kings will essentially.

I'm prone to believing that Mu Deok's soul is special but incomplete because she might be a daughter of a powerful magician family aka the Jin family. She instinctively captured Naksu's soul into her own body when Naksu tried to Soul Shift. Now, Naksu cannot access her powers not only because the body is weak but also because Mu Deok is using Naksu's energy to heal/complete her own soul. We actually have evidence that the reason Mu Deok is blind is soul related evidenced by the body no longer being blind when Naksu's soul takes over. My theory is that Mu Deok's soul is slowly absorbing Naksu's in a dormant state and will eventually become more active as time goes on since her soul will be getting stronger and stronger with Naksu's energy. We see her become more active already in episode 5. Her eyes are also pretty normal still, meaning that her soul might have already been replenished enough for her to see normally (Though we don't know for sure).

I have a theory that her case is different. My guess is that she won't because her case is 2 souls in 1 body where the original soul is still there, only dormant for the most part. I think Naksu's soul is currently dominant only because her soul is more powerful. However, as time goes on, her energy is feeding into Mu Deok's soul, making it more complete. (I previously made a theory explaining why I think Mu Deok's blindness is connected to her soul being incomplete/damaged.) Naksu cannot access her energy because it is nourishing Mu Deok's soul. In episode 5 we actually see that Mu Deok is slowly gaining more control when she awakens in control of the body when Naksu is asleep. When she awakes she has no recollection of being awake and seeing the fight between Jang and Lee.

In essence there are 2 reasons in which I don't think she will run wild. (Unless she somehow loses Mu Deok's soul). The 2 souls seem to be feeding off of each other in which we see a positive feedback from Naksu to Mu Deok. As to whether Naksu receives any benefits to this exchange is to be seen. However, according to my theory, it is unlikely that Naksu will have a need to feed off energy from other humans as the original soul still sustains her current body.
The other reason is based off my theory that Soul Shifters require a constant supply of vitality replenishment because of the incompatibility of a foreign soul in a foreign body. When ones original soul leaves the body, an opening appears in the body (probably what the blue circle that indicates one being a soul shifter) aka an open door. When a foreign soul enters that door, they do not have the ability to close it because they are not the true owner. Thus they are susceptible to wear and tear. At most this is better than not having a body, which will probably wear the soul down MUCH faster. However, with the door to the body open, the soul still gradually wears down. Thus they have to absorb others souls to replenish their own. Basically filling up a leaking container.

Naksu and Mu Deok has no need for this because Naksu's soul was instead 'welcomed' or rather 'captured' by the owner of the body. This is also why I believe that Mu Deok is the daughter of a powerful magician family (Probably missing Jin daughter). It might not have been intentional by Mu Deok herself but an instinctive reaction to 'complete' her soul. This explains why the body is no longer blind by the time Naksu takes over. She doesn't have the blue circle marking that other Soul Shifters do. This is because the door to the body was not left open and thus the soul will not wear and tear. The blue eyes appearing is most likely due to a physical manifestation of Naksu's energy being absorbed by Mu Deok's soul. We actually get to see that there is a certain exchange/connection between the 2 soul's through a line connecting the 2 souls whenever we see the 2 in their 'Soul Matrix' as I call it.

I am almost positive that Naksu's father got killed due to him being a soul shifter at the time. That explains why the maid told Naksu to run away from her father and why the Songrim ppl killed him. It also explains the coincidental finding and adoption of Naksu by the Jin guy as an assassin.

I don't necessarily think that Mu Deok's soul will end up completely overpowering Naksu's but I think that something will happen when the 2 soul's eventually reach a certain equilibrium as my theory stands on the idea that Naksu's soul is currently more powerful than Mu Deok's but Naksu's energy is feeding into Mu Deok's soul.

I am starting to think that Mu Deok is the missing eldest daughter of the Jin family. If memory serves me right that was a thing that was mentioned in a previous episode. The preview of episode 6 suggests that Naksu in Mu Deok's body visits the Jin family household and seems to recognize it somehow, suggesting that either Naksu or Mu Deok have some sort of connection to the Jin's. We know that Mu Deok's soul is still in the body. Both soul's seem to coexist together in the same body which is probably why Naksu seems different from other Soul Shifters and does not need to constantly replenish her vitality.

Heres my theory on this:
The reason Soul Shifters must constantly replenish their 'vitality' is because shifting souls into another body makes it incompatible and prone to leakage/damage over time (kind of like oxidation). The body at most serves as a temporary husk that slows down the weathering of the soul compared to not having a body at all.
Naksu's situation is a bit different (though not yet explained how and why) because Mu Deok was born with a 'damaged' or 'incomplete' soul. That is why she was 'blind'. (There is a saying that the eyes are a gateway to ones soul.) When Naksu tried to shift into someone else's body, she accidentally shifted into Mu Deok's. It isn't yet explained why that happened, but I have a guess. For the guess to be more plausible though, it would make more sense if Mu Deok came from a bloodline of powerful magicians, which might cause her soul to be a bit special as compared to normal humans the moment she is born. When Naksu tried to shift bodies, Mu Deok's 'incomplete' soul attracted Naksu's soul over to make it whole. This is why the body is not longer blind. When the container for the soul is complete, the body too will become whole. Another reason Naksu's body does not breakdown and need replenishing is because Mu Deok's soul is still there. If the original soul is still in the body, then the body has not need to breakdown. Technically, their souls weren't swapped, Naksu's just entered Mu Deok's and became the primary controller. Probably because her soul was more powerful than Mu Deok's. Of course this doesn't explain why Naksu can't access her powers. However, I think as time goes on, Mu Deok will gradually take back control little by little. We saw in episode 5 how Mu Deok took control temporarily when Naksu was asleep. My guess is that Naksu's energy is slowly feeding into Mu Deok's soul instead of Naksu's own which could explain why she can't access her energy. Whenever we see Naksu and Mu Deok in their 'Soul Matrix' we see a line of energy connecting the two.

Of course there is another possibilty in which Naksu' memories were altered from childhood and she herself is the daughter from the Jin family. However, then the prominence of Mu Deok the blind decreases a lot more and would need another explanation on why Naksu and Mu Deok are different from other Soul Shifters.

So my predictions were on point for the most part. I read the killer's personality pretty on point too. Only thing was that he's abusive to his daughter even when not drunk. He kept the daughter alive because he wanted to feel in control. He needed someone for that, whether it was his wife or daughter. As to why exactly he killed his wife, we don't completely know and it was never revealed. I think it was kind of sort of hinted that the wife discovered his secret, but its not completely confirmed that thats why he killed her. My first theory initially was that he was a serial killer who moved in to town a few years ago and thus why there werent any noticeable news of people dying left and right initially. But then I changed my stance on that he might have started his killing spree after "accidentally" killing his wife, but that would be in direct contradiction to him killing his wife because she discovered his secret. Thus, my first theory is more likely to be correct about that. I also think that my theory about him marrying his wife to basically "buy" a tool to make a child of his own is more likely than not to be correct. Though he probably didn't kill her because she was cheating on him or that she wanted to leave him, but rather she found out he was a serial killer. Its harder to control an adult than a child who you have greater influence over, which is why he killed his wife and not his daughter despite the finding out that his daughter discovered his secret. He needed "toys" to play with and control. In a way, his victims were temporary toys for him to satisfy his greater needs to feel in control when he feels depressed about his life. His wife and daughter on the other hand were more "permanent" toys to remind himself throughout his daily life, that "yes" he is in control. He finds easy targets to kill during the times he feels like he isnt in control (aka times when life sucks). The fact that he likes to abuse some of his victims proves this point. In a way, for him, murder and abuse is a way for him to relieve his stress.

He threw a can of peaches at the con man when he was choking his mother out. The can broke the guys head and he bled a ton. They were left to believe the guy died and the trauma stuck with DS.

I reckon that for her to be able to manipulate time, she would have to risk erasing her own existence. So I think that in the new timeline she will die eventually, but this time, her soul will be erased. Makes more sense that way. She put her hopes of vengeance on KHW, giving him a 2nd chance to make CTS suffer and in return, she sacrifices herself entirely.

So its been all but confirmed that the realtor is abusive. Most likely he becomes abusive when drunk. I am really beginning to think that his missing wife was in that freezer in 408 and chairwoman was attacked to shut her up. When we see him find Yul with the others, he has a cut on his chin. The same cut is on Meat's chin when he accidentally hurts himself with a glue gun due to DS's surprise of him holding it when he wakes up from a nightmare.
Heres my theory:
1) Realtor marries a foreign woman from Vietnam. Perhaps even 'bought' a wife from Vietnam. Probably did so only to have children of his own. He likes control.
2) He beats his wife and daughter when drunk. Yul has a somewhat odd relationship with him. Sometimes she appears afraid to tell him things but sometimes she clearly sees him as a support. This is not an odd behavior if he is usually nice to her. He probably beats her only when drunk.
3) Wife probably cheats on him or plans to leave him. He kills her before story begins and hides her body in 408.
4) His life has gone downhill which is why he always looks rather depressed. He drinks more and beats Yul. This is why Yul always has injuries.
5) After the incident with his wife, and accidentally killing her, he develops a certain anger for certain women and begins killing them. The stockings he used to kill victim #1 might have been his wife's or stockings that she liked to wear. I think he is developing his M.O. or rather it might not really matter how he kills them. He just wants them to suffer before dying. Thats why he glued chairwoman's eyes and mouth shut before attempting to kill her. He likes the feeling of being in control. Yul's behavior around him could be indicative of his manipulative nature in trying to maintain his control. Thats why he tells her not to trust kind adults (aka our MC and his crew). He wants her to only rely on him. This is also why he probably killed his wife. He was no longer able to control her.
* It could also be that his wife never planned to leave him and he just accidentally beat her to death. And that feeling got him hooked on murder.

Realtor is definitely related in one way or another to the murders. He clearly knows about the apartment that no one supposedly lives in. And lets not forget that he has access to the apartments as we know from the 2nd victims case. So either he is the killer or the killer is someone close to him and he is protecting them aka his mysterious wife.
Veggie was attacked by someone with a knife who someone knows the passcode to her apartment. This is only possible if the person has been either stalking her for quite some time, someone very close to her (Unlikely), or its the realtor/related to him. The killings in that building have a relatively small time gap in between so I don't think its a stalker who has been stalking her for some time.
No matter what the case is, the realtor is related one way or another.
As for Yul, I think she did indeed witness something. She has been sending mixed signals to viewers with her dad. When questioned about the murder by "Fish", she keeps looking at her dad, indicating that she definitely knows something about it as she is visibly nervous when questioned. Her constant eye signals toward her dad indicate that he is related to the murders. However we don't know if he was the direct killer or not.
The phone she is trying to hide seems to be a key evidence of sorts, but she also states to the conman that it was her mothers. She also questions her dad about when her mom will return, in which the dad kind of brushes it off.
When the chairwoman goes to his office and get into a fight with that other lady, she also mentions about the empty apartment using electricity when no one lives there and he has a slight change in his reaction and then gets annoyed and outraged as if he was triggered. So he definitely knows theres something wrong with that apartment, does not do anything about it, and does not want anyone to notice or mention it.
He is in a rush to get home when Yul is found and then questions her about what she witnessed and then tells her not to get close to the MC. I think he knows how observant the MC is and is afraid that he will notice something wrong about him the more Yul opens her mouth to him.
Between the realtor or his wife, one of them is most likely the killer. I am crossing out anyone else on my list because there are too many points that indicate his relation to the murders.