So far we have seen that Kang Chul possesses free will that goes beyond the prescribed narrative and personalities that his comic book creator made him.  It makes him dangerous and uncontrollable.   Besides having the will to change the plot of the comic to remain alive in the narrative and write his own story, the shooting of the main heroine also proves this point.   YJ didn't believe he could shoot her because of his character that she read in the comic thus far,  but he did, betting on his instinct to prove a point despite the danger to her life.  This makes Kang Chul a truly dangerous character, maybe a monster like her father thought.  He is willing to go beyond scripted personality and predictable acts to test his theory,  shooting a person who repeatedly saved his life so far in the heart.  Kang Chul could have chosen a different target, her leg, arm or something, at such a close range it is possible, but he risked it and shot her through the heart just on instinctual guess.  He is risking the life of a person who saved his life just to prove a point and wanting to solve the riddle of his existence.   This makes him extremely dangerous and unpredictable.  

I know the story is one of comic book fantasy but the I just can't get my head around YJ not seing this shock of being shot and recover so quickly.   How can she trust him if he is willing to risk her life to find out the truth?  Maybe because she is so blinded by the adoration of his perfect comic book looks and character that she fails to see this.  My guess is that her father created a character out of her deepest yearnings for a perfect man that's why she is so madly a fan of him trying to desperately see a good ending to his story.  He isn't your typical one or two dimensional comic book character when free will is involved.  It makes him dangerous and even more alluring.  She doesn't see how dangerous and unpredictable he had become like her father saw.  This again could be something women are drawn to, the main character with a little dangerous dark side.  With her boring life as a medical residence who is overworked with little sleep,  this proves a good escape from the mundane.

Free will is dangerous, it also makes for a good character which drives the plot of this story.

I can guess from the preview of episode 4 that he would likely set her up to be caught by the police and in a desperate situation to get her to tell the truth.  It almost makes me cringe where the writer of the show can take his character from the act of desperation to find truth and continued existence.  Certainly Kang Chul is not one dimensional like most Kdrama characters, or I hope the show writers won't turn him into one later.  Kang Chul dangerous free will is intriguing to watch and he certainly drives the plot to make it interesting.
I also felt uncomfortable with how quickly YJ accepted Chul's apology. She didn't know she was invincible in the world of W. As for Chul, I suspected he knew she couldn't be killed; either because of his inkling that she didn't belong to the same dimension, or because of the almost-collision with the truck where he saw everything stop. In any case, it did the job of creating tension and suspense for the episode. It also illustrated what Chul is willing to sacrifice to discover the truth and mark how serious he is. I guess when you try to accept the fact, it plays to the characters' oddities. Like Doo Yoon and Soo Hee, we find them strange and their relationship incomprehensible. It works. 

However in terms of free will, instead of viewing it as dangerous, I think it's meant to be empowering for Chul. His life has been shaken up inexplicably so many times, he finally realises he can take control. I wouldn't paint it as being dangerous. That's the authoritarian argument which should not be the norm. However, I see the confusion given we're straddling between the real world where free will reigns, and fiction where the will of the author is controlling.
In episode 5, we again see Kang Chul being capable of free will going beyond his prescribed character.  He shoots knowing that he could kill the author of his comic in real life.   When he was told that he was created as a comic hero who is a good guy and incapable of shooting a defenceless old man, he took the shot. He knew full well that it can kill the author, OYJ's father.  He did this with complete disregard for OYJ who saved his life many times and loves him.  Certainly I would think twice about killing the man of a girl I like, or the one who saved me.   Not in this case,  KC free will gave him the ability to be out of character and its associated morals.   This is truly dangerous when one no longer operate out of a set of moral or character values.   The author of the story was merely creating a story to pay for his drinking habit and his daughter's care,  it wasn't motivated by anything sinister but just good fiction writing.   The main character cannot have a happy life because angst sells the books.  Too bad he had no idea that an imaginary character whom he created will come out and shoot him in revenge for his creating so much pain and a fictional universe.  To be a little more philosophical, if we all one day encounter God who created all the life and everything we ever experienced, will we shoot him because we have free will not to accept what happened?  That it was all a fiction, even though the sufferings and pains feels real?  KC is experiencing this existential crisis where his life has no meaning and the culprit of his family's murder doesn't exist.  His whole quest for revenge was just a plot that was driven by the senseless and meaningless death of his family, a device to drive a plot to create a hero character.  When free will goes beyond values of good, operating beyond society's norm, it is dangerous.  KC once again proves that he is dangerous and capable of becoming a real monster.  Capable of killing and harming out of spite and not goodness.  Hopefully, there is some redeeming quality left in him, otherwise I don't see how OYJ can love a person who had not only shot her but her dad as well, with the full intention of harming.