There’s a time crunch so I’ll keep this short.

1. The mystery mage

A mysterious mage suddenly appears in the Jinwoyon. He calmly dispatches the female guards at the Jin’s manor by temporarily incapacitating them. He tells the unconscious guards, “Stay down for a moment.” This is a good sign. It means that he isn’t blood-thirsty.

He then stands outside the Jin’s family vault and summons Gwiju, the dog spirit.

For now, I’m going to assume that he’s the other person Heo Yeom remembers as having achieved the “alchemy of souls.”

Yul: (talking about the soul shifter) He is no different from an evil spirit. I can see why you forbid this sorcery.

With this mindset, Yul isn’t disposed to being kind to Naksu/MuDeok if and when he discovers the truth about her soul-switching. Unlike Uk who was in need of Naksu/MuDeok’s service to open his gate so he was willing to take her in as a master, Yul would have no qualms killing her off as he views her as similar to an “evil spirit.”

HY: The alchemy of souls was not a type of sorcery from the start. You can only perform this once you have mastered Jipsu, Ryusu, Chisu, and ultimately, Hwansu.
DongGu: Hwansu is the godlike power of changing water to fire and vice versa. Is it not? Humans cannot reach that level.
HY: Right. But Master Seo Gyeong, the founder of Songrim, did. There was also someone else.
DongGu: Who?

Lol. DongGu’s inquisitiveness is to be expected. He ends up acquiring more information than the rest of the Four Seasons kids, since he likes to listen to rumors.

Heo Yeom retorts that DongGu’s not likely to know his name anyway.

Then, in the next scene the mysterious mage appears at Jinyowon.

His skills must be at god-level then. But as I said earlier, I don’t think he would be out to get Naksu/MuDeok should they encounter each other. He’d probably be empathetic of her situation. I see him as her ally and Uk’s.

Also, as I wrote to @Fern, I believe Master Seo Gyong, the founder of Songrim, and that anonymous individual with the Hwansu level of skills, were able to perform soul-shifting/alchemy of souls WITHOUT the use of a device. My sense is they can achieve it through mastery of their magic skills, i.e., through a natural progression of their magical skills.

In contrast, Jang Gang acquired his soul-shifting ability through experimentation. Remember that mom in the opening scene in Episode 1? She said it was Jang Gang who did it on her son. When she said, “You were the one who turned my son into a soul shifter,” she sounded accusatory, like it was Jang Gang who first approached them and proposed to do the experiment of her son.

My guess is he was using people like lab rats to perfect his “Soul Ejector” device. He already had 8 failed experiments. In Episode 3, he told Jin Mu to bring him the “Soul Ejector” from the Cheonbugwan Secret Room.

As a “payment” for helping him out, Jang Gang promised to teach him how to shift souls/alchemy of souls. He passed down his method of creating this Soul Ejector to Jin Mu. In turn, Jin Mu passed down the technique to Naksu. That’s how Naksu ended up with a Soul Ejector in her hand to shift soul when she was dying.

To borrow @Fern’s word, this Soul Ejector is a “short-cut” to performing the soul-shifting. The original mages were able to perform the alchemy of souls by their own powers and unassisted by a device.

2. The ice bath 

The old-timers on this blog know that I prefer writing down the dialogues so I can parse their words and get the nuance.

To me, the bathtub scene is important for two reasons.

a. First, it shows what a “torrent of energy” can do. Naksu explains the changes in Uk’s body as the energy surges and recedes, and she tells him what he needs to do.

Naksu: It was the flogging. It caused the torrent of energy to surge faster. (smacking him) I’m glad you got flogged.
Uk: MuDeok, I’m burning up.

Just one small point. Uk has always called Naksu by MuDeok’s name. I like that because a new name symbolizes a new beginning. Uk is getting her accustomed to her new life.

Naksu: You will burn up once the torrent of energy transform into heat. Then you will feel chilly when it becomes cold. The energy will be yours only if you can bear that. Keep breathing slowly.
Uk: (nodding)

Naksu draws water from the well. It’s cold water. Notice that when she scoops water from the well, there’s no steam rising from it.

However, when she dumps the bucket of cold water on Uk’s back, there’s steam. This tells us that his body temperature is so high that he can heat up cold water to boiling point as soon as it touches his body.

That’s how hot Uk’s body has become. (hahaha. I don’t mean in a sexual way, okay?)

Boiling water is 100 Centigrade of 212 Fahrenheit.

Later, when Naksu returns from the well with DoJu, Uk’s surrogate mom, they were both surprised that the bathwater is freezing cold.

Only Naksu knows that the freezing cold water was boiling hot when she left Uk in the tub. She puts two and two together and realizes that Uk’s energy has changed while she was at the well to fetch water. His body has become cold, so cold that it turned the steaming bathwater ice-cold.

Because of his low body temperature, he’s in danger of hypothermia. Naksu doesn’t want him falling asleep. A hypothermic person is known to just go to sleep before dying.

Oddly though, it’s fine when she lulls him to sleep with her “heart-warming” stories. I think that’s because her “heartwarming” stories literally makes him feel warm inside, but at the same time, they help him calm down. Remember, to control the energy surge he needs to breathe in slowly. His breathing slows down when he goes to sleep. Also, the slow rhythmic pats on his back also helps him to regulate his breathing.

b. the bathtub scene is also important because it connects Uk to the story of his birth.

King: Do you remember the divination I received on the day of my coronation? You said I would be granted a son who had the energy of the King’s Star.
Jang Gang: The divination was incorrect. That cannot be.
King: No. What you said has to be true. I will have a son thanks to your alchemy of souls. Remember that. Dohwa will bear my son. He will be mine.

Then, sure enough on the day Uk was born, the star appeared.

The astrologer saw the star at the center of the Big Dipper that contains nature’s secrets. It only reveals itself when the sky is filled with the energy of the Daeho waters.

Here’s how the Big Dipper typically looks like.

Here’s the Big Dipper on Uk’s birthday.

Visually, the image Uk sitting in a bathtub brings to mind the King’s star at the center of the Big Dipper.

After all, a dipper is just a water container with a long handle. MuDeok dipped the bucket into the well to fill the tub with water, Daeho water, just like in the prophesy.

Like the King’s star that contains “nature’s secrets,” Uk’s birth is full of secrets.
And like the sky is filled with energy of Daeho waters, the bathtub is filled with the water heated from torrent of energy surging in Uk.

Do you get the visual parallelism?

That’s why I think this ice bath is a great scene.

3. An act of stupidity or vigor

Naksu wakes up to see Uk contemplating his sword.

He’s recalling Park Jin’s words. He told him, “You cannot even take out your own father’s sword. How do you expect to learn spells? No one in Daeho will be able to go against your father and open your gate of energy. That was the fate given to you by your father.”

Replaying those words in his mind, he struggles to unsheathe it. Naksu speaks up.

Naksu: You are not ready yet. To unsheathe a mage’s sword, you must master Ryusu and be able to channel your energy outward.

Remember now: Ryusu is the second level. It’s Jipsu, Ryusu, Chisu, and now we hear, there’s Hwansu. The Crown Prince and Yul are at Ryusu level.

Naksu: You cannot do it just yet since you cannot control your energy.
Uk: My father left this sword behind when he abandoned me. And I can only join Songrim if I unsheathe it. I want to unsheathe it and show them.

In particular, he wants to show Park Jin.

Uk: Is that an act of stupidity?
Naksu: No, it’s an act of vigor. Stay strong, Jang Uk.

The subber translated 기세야 or “giseya” as vigor. I think there are better words like zeal, zest, drive, determination, passion, motivation, spirit, fire-in-the-belly.

I’m focusing on this word because one of the techniques of the Hong sisters is to throw a random word or catchphrase out there, and then build a plot around it to explore its different nuances.

For example, in Episode 1, the word that was said repeatedly was “master.” Uk was looking for a master, one that fits his needs, so he defined what a master was to him. In the end, he found Naksu/MuDeok.

In Episode 2, the concept was loyalty vs duty. When Naksu poisoned Uk, her motivation was a mixture of duty and loyalty. She needed Uk’s GOE opened so she could get her own energy back but at the same time, she wanted to help him out.

Now, in this episode, it’s about “giseya” or vigor, zeal, zest, persistence. Naksu doesn’t think that Uk’s determination to prove himself at the Songrim is stupid. On the contrary, she approves of him having a strong ambition and striving hard to get it. Hence, she encourages Uk to “stay strong” as he pursues his goal.

What’s the difference between an act of stupidity and act of vigor?

Well, stupid is stupid. But an act of vigor isn’t foolhardy. An individual can be passionate and zealous about attaining his goal, but he can’t be reckless, rash, and stupid about his methods to achieve it. His actions must be purposeful.

4. The duel: act of stupidity or vigor?

Later, when Uk duels the Crown Prince, Uk brings it up.

CP: You are not fully trained for a true fight. (drawing a line on the ground) If you can push me over this line, I will leave.

Uk takes a step toward him, but MuDeok holds him back.

Now viewers may understand Uk’s movement differently, but this is mine: I think Uk was offended by the Crown Prince’s words.

The Crown Prince was looking down on him. It’s okay to acknowledge that his opponent is inexperienced. But it’s not okay to tell him that he’s such a weakling that he can’t even budge him. The Crown Prince is conflating inexperience with frailty.

His words naturally provoke Uk who’s already upset about his father’s sword being taken from him. He’s just going to charge at the Crown Prince without a thought. But MuDeok’s restraining hand brings him to his senses.

The Crown Prince observes their interaction.

MuDeok gives Uk a look, and Uk nods his head. MuDeok then releases him.

So what did she tell him? No. She wasn’t telling him, “Fighting!”

In my opinion, the looks exchanged between the couple is not a romantic one. Neither is her hand on his wrist a romantic skinship. They’re simply a nonverbal communication between master and pupil. She’s reminding him to refrain from acting stupidly.

That’s the impact of MuDeok on Uk. With just one look, she gets him to behave, to be deliberate, to be purposeful. Uk walks up to the Crown Prince.

Uk: I am sure you expected me to grovel in humiliation. Going against you would be an act of stupidity. However, there is someone who sees it as one of vigor. So I shall try.

By “someone,” he’s referring to his master, MuDeok, of course. And by “I shall try,” he’s illustrating the essence of giseya, not stupidity. He has his master’s approval to duel the Crown Prince.

4. Lack of vigor

But like his torrent of energy can surge and wane in a heartbeat, Uk’s vigor can come and go easily in a heartache.

Park Jin’s revelation about his paternity extinguishes his giseya and deflates his spirit.

Uk: Then I felt a surge in me. That is when I unsheathed it.
PJ: Right. You were always a quick learner compared to others. You even learned to walk and run sooner than Danggu did. You could also talk before he could.
Uk: I still remember that. When I did not know what it meant to have a blocked gate of energy, I thought I would become the most powerful person.

He says this so innocently because he’s oblivious to his full potential and to his fate. He can indeed become the most powerful person now that he’s GOE is unblocked. His words had a chilling effect on Park Jin because he’s aware of the danger.

PJ: Uk. You are intelligent and pick up things quickly. How about you join our trade and learn how to do business? Or Master Heo can take you under his wing and teach you the art of medicine.
Uk: No my lord. I am going to train in Jeongjingak and become a mage.

Here’s his vigor/giseya on display. He’s resolute. Naksu would’ve been approved of this.

PJ: Why? Because that is what your father did? Do you desire to become the next Gwanju of Cheongbugwan?

To me, Park Jin made a wrong move. He shouldn’t have answered his own question. He should have listened to Uk after he asked “why?” and remained calm. Instead, he comes out confrontational. Naturally, Uk bristles.

Uk: (defiant) Yes, my lord. And I will be. I will take his place and prove it to all those scumbags who denied that I was his son. I will make them speechless.

So Park Jin decides to make Uk speechless instead.

PJ: You are not his son. You are the result of your mother’s love affair. To show our respect to your late mother, we let you into the Jang family. But we cannot allow you to lead Cheonbugwan after your father. So stop dreaming of becoming your father.

Lol. Be careful what you wish for, Park Jin. Personally, I think it’s better if Uk continues to dream of becoming like Jang Gang than becoming like his real father, the former King.

PJ: (continuing) Just stay a clueless Young Master of the Jang family. If you do, we will continue to take care of you.
Uk: (tearing up) Then, then who is my real father?
PJ: How would anyone know whom your late mother had an affair with?

I know it hurts Park Jin to slander DoHwa like this. But again, he thinks this is the only way he can protect Uk. He must break Uk’s will by any means possible to stop him from meeting his fate.

And Park Jin succeeds.

After Uk is told the lie that he’s a result of his mother’s affair, he loses his zeal/will/giseya/vigor to prove to everybody that he’s his father’s son.

But when Naksu sees that his food has been untouched and that his body is still lying inert inert on the table, she calls him out for self-pity.

She approves of Uk’s vigor so conversely, she deplores Uk’s inertia and apathy.

MD: I cannot tolerate this any longer. How long will this pity party last?

She tries to pull him up.

MD: Get up!

She kicks him for good measure. She thinks he’s down on himself for accidentally stabbing Park Jin. She misunderstands the reason for his silence because she heard Yeo Heom and DG consoling him about the accident. YH and DG were actually rubbing salt on his wound when they a) praised his skills while misattributing it to his father, Jang Gang, and b) reassured him he’d still become the next Gwangju of Cheonbugwan because he’s the eldest son of the Jang family.

Hearing these, Naksu thought he’s self-pitying for no good reason. She’s unware of Uk’s earth-shattering discovery.

MD: You received a powerful torrent of energy and it surged within you. It took you merely ten days when it would take ten years for others. If you keep training…
Uk: Forget it. I will not do it.
MD: Have Park Jin’s few words dispirited you? So all this was just an act of stupidity? No wonder you look so hopeless. You are just too weak!
Uk: Yes, I am. So I am not going to do anything. So just be quiet. Just shut up and do not bother me.
MD: I do not need a pupil who will not do anything.
Uk: Then do not be my master. Just be my maid. Annoy me again, and I will sell you off.

Then he lies down again.

So she maneuvers the situation to get him out of his malaise. She pushes for another rematch between the Crown Prince and Uk so Uk will be forced to get up and regain his vigor/giseya/drive/ambition.

Uk: Were you behind everything?
MD: I just played a part. You finally budged when I said you were in danger.
UK: (huffing in annoyance)
MD: What is wrong? I do not need a pupil who does not improve. Just die if you are not going to do anything.
Uk: You have poisoned me again, crazy master.

By hook or by crook, MuDeok wants him to get his mojo back.

5. The Secret Room’s broken door – I saved this till the end.

MD: Did he scold you again? I thought you were used to being scolded.

She stops because she sees his tearstained face. She moves away to give him privacy but then the Secret Room’s broken door begins to lock them in.

MD: It was not me. I do not think they have fixed the door since that incident.
Uk: Do not move. Just stay there. It might all crumble down. So just stay there.

Uk continues to cry.

I thought that was great metaphor. On the surface, Uk is simply reiterating what needs to be done when the Secret Room’s door activates. The ground will cave it when they make a move so they have to stand still and wait until the door fully closes first. He’s reminding MuDeok not to move.

But there’s an inner meaning to his words now. His words are not actually meant for MuDeok alone. They’re meant for him, too.

Park Jin just told him that he must stay a clueless Young Master of the Jang family. If he does, the Jang family, Songrim and the rest of the mage world will continue to take care of him.

But if he moves, then his world as he knows it will all crumble down — like the Secret Room.

Thus, he’s crying because he has to let go of his giseya, and just literally and metaphorically, stay there.

That’s what I think the next episode will be. It’s about Uk’s retreat and tacit submission to his Park Jin’s wish to stay as he is to do no harm.