ok after reading theories about The King: Eternal Monarch, here's my take:

Let's start with the theories I've read so far:
1. TaeEul will die
2. Time loop
3. LeeGon is his own savior
4. ShinJae is LeeGon's savior
5. Another universe

I'm going to discuss the theories by number. I will either support it or debunk it- will also explain it. This is my analysis and opinion, okay?

First theory is a big possibility. I'm going to support that theory. Not going to explain why anymore bc you can easily read the theory itself online and it nailed the explanation for the metaphoric details about TaeEul's death. I believe they will try to save her tho.

When they learn about TaeEul's death, they will want to save her. LeeGon will do everything hence the time loop theory and the title Eternal.

I support the second theory as well bc if you noticed, TaeEul's ID was from the parallel world(Republic of Korea) and LeeGon's savior had it with him. The ID was issued in the year 2019 & the shootout happened in 1994. Someone from 2019 came back in time to save LeeGon.

Third theory can be literally taken as, LeeGon is his own savior meaning he was the shooter and he came back in time to save his younger self. That's what other people think. I saw a few tweets supporting this but---

I don't think the third theory should be taken literally. Instead we should try to look for its other meaning. Third theories' other meaning makes more sense hence I will not debunk the third theory. The next tweet will explain why.

It is certain that he will do everything in order to stop or undo his beloved's death. Thats why he needed to live. BUT we all know he is not the best at shooting. His savior was a great shooter. I think he saved himself by sending someone back in time to save his younger.

Meaning third theory is still reliable- it's just that, it shouldn't be taken literally. Ok so who did he send? It is not TaeEul herself because of the obvious built of a man. It is not captain jo as well bc it wouldn't explain why he had TaeEul's ID.

ShinJae must be playing a big role on all of this. He is a police officer, good at shooting, he is one of TaeEul's close friends, and is in love with her. He will find out about the parallel world soon.

Fifth theory suggests that LeeGon's savior is ShinJae. In order to save himself, LeeGon has to send someone back in time. He couldn't do that himself for obvious reasons.

I believe LeeGon finds out about the fifth theory which is another parallel universe. This is where it gets crazy. He gets to see what the world would be like if he died that day in 1994. His uncle spread havoc and rule both worlds. You get the picture.

Tying it all up. In order to sustain the balance of worlds and save TaeEul, LeeGon has to think of a plan to save his younger self. This is where ShinJae comes in. LeeGon shows him the aftermath of what will happen if he did not save him.

LeeGon needed to live in order to become the king, rule, meet TaeEul, save her and both worlds. It all led to the same event, he was bound to live through. Also,
im sure he stopped aging like his uncle. He is eternal metaphorically and literally.

Quite ironic for ShinJae because in order to save his beloved, he had to save her beloved.

What do you think? Do you have any questions? What's your theories?

Ok so im back with supporting details:

-ShinJae is from the Kingdom of Corea
-He lost his memory
-He recognized the symbol(Flower)
-He has nightmares