The premise itself is good, and the characters in MC's new world are interesting, especial So Won. If it's going to become *cough cough* BL *cough cough cough* I'd eagerly be following along. It's fine if it's not, though, I could just silently ship the characters from the safety of my couch ^0^
I read past chapter 3, and though there were still some tricky parts, the writing becomes much better from there. I strongly recommend for any author to use Grammarly before publishing (and no, I'm not getting paid to endorse it this damn much). I have it installed in Chrome, it's my last line of defense before releasing a chapter.
Here, there were still minor errors in the first two chapters that I didn't address because I'm pretty sure the free version of Grammarly would catch them just fine. That said, author, please take this as a gesture of goodwill because I saw in the forums how worried you were--
Chapter 1:
lion and his songs that
--> and WITH his songs that
the 75,000 seats in the stadium were full
--> were FILLED (to capacity).
Kim Chun Ha appeared on stage
--> make it "onstage" -- no space
a 19-year-old boy with black hair and green eyes of 179cm entered -- like this, it sounds like it's his eyes that's 179cm, so...
--> a 19-year-old boy OF 179cm, with black...
they needed to take a sleep
--> EITHER needed to sleep OR needed to take a nap
Jae Hyun decided to tell HER
--> tell HIM
In fact, I have already informed...
--> you forgot to add the opening quotation mark "In fact...
Do you even know dance? And just saying but when you agreed to give me your voice
--> Do you even know how to dance (not sure if this is what you meant, but "know dance" doesn't sound right)
--> make the next statement stronger by simply starting with "When you agreed to give..."
--> delete "and just saying"
He ignored what he had just told him before look at him and talk.
--> (Jae Hyun) ignored Chun Ha's words (I'd suggest naming at least one of the characters in a sentence if they have the same gender; it's to avoid confusion about who's doing what)
--> and simply looked at him before speaking.
Kim Chun Ha's anger lashed his mind and blew up.
--> I don't understand what you mean by "lashed his mind." Maybe it's best if you just say (his) anger blew up.
I make you regret being born
--> I'LL make you...
a shot was heard
--> a shot sounded OR rang out (to avoid the passive "was heard")
Once he would be cured
--> Once HE'S cured
Jae Hyun had a pinch in his heart
--> Jae Hyun's heart constricted
Chapter 2:
He tried to sit down,
--> sit UP
his body gave up to him
--> up ON him
his agencyβif you say soβsaved
--> did you mean "if you could call them that"?
Fake to sleep? Hid?
--> Fake sleep
--> Hide
Think to something
--> Think OF something
and the panic gradually spread to him
--> and his panic gradually spread (could use a different word here imo).
He was going to tell them their home truths!
--> "home truths" seems to be an idiomatic expression in French? Not sure, but it doesn't translate well, I would suggest a more common phrase like "tell them what's what"
Sorry I didn't force you.
--> Sorry, I shouldn't have forced you/pushed you too hard
"Am I still dreaming?", though he.
--> he thought.
--> a comma is not needed if the dialogue itself ends with a punctuation mark
Great, already that he wasn't very tall
--> ...he wasn't very tall to start with
Was it a contribution for being jealous
--> ...a retribution for...
What year and date are it today
--> What year is it? What's the date today?
---
That's as far as I've gone editing. I really hope this would be of some help, it's not my intention to make you feel pressured or anything, but I'm sorry if that's how it turns out.
Best of luck from here on out as well :)