I could agree to some degree. They are probably in a time loop where they both migrate. And only Iheon knows about it.
Iheon probably wrote the book and then showed it to Huimin as he mentioned his friend told him about the book with an Huimin that has the same name as him. The writer of the book is also shown as circle. Probably when Huimin didn't take interest in reading the book still, he got his sister involved and sent him the book himself.
I think Iheon keeps going soft on him bc he realized Huimin remembers the book this time around.
He probably knows when the alt universe story begins so he tries to talk Huimin in going to America but Huimin always declines. This time too he insists a lot but got turned down again. They probably enter the alt universe at the same time but at different times in the alt universe. Iheon probably enters first and suffers bc Huimin acts distant and something always happens.
Huimin over the loops never told Iheon about the cause of his trauma, but he did this time. And the other small things he does bc he knows about the story is what keeping Iheon sane and trusting to an extent.
Want some spoiler? (≧∀≦) Just a rough one not a full spoiler
dude i love your take *chef's kiss*
YES LOL, PLEASE HIDE IT TOO
Oh, spill, spill, spill.... ε=ε=(ノ≧∇≦)ノ
You can read the spoiler here: It's a full one, not a rough one (≧∀≦) I'm just to lazy to type it back ..
https://www.mangago.zone/home/mangatopic/16637253/
1. Iheon (20s) must've been the first one to get transmigrate inside the novel and has been living a loop since Iheon (20s) and Iheon (30s) likes has been overlapping as we could see from Huimin (20s) perspective. Now that Huimin (20s) is now here, he might be the catalyst for the time looping of Iheon.
2. The novel that Huimin (20s) had read might be their parallel life that they get to live as well before coming to the world (where they are just normal people without any tragic background, where Iheon (20s) is just rich lol) that they now live in. They might not have remembered it but now that Huimin (20s) have read the novel, he's living on it again because he transmigrated inside the novel.
3. Iheon and Huimin (30s) is stuck in a time loop and everytime they both die, Iheon was the only one who could remember it. Huimin (20s) might also be the catalyst to break it since he came from a parallel world.
4. This story might've been just Huimin (30s) remembering his first life and had just committed to that personality because he'd probably break if he remembered the other lives he had or he just really don't remember it, only Iheon (30s) remembers everything.
I think the biggest clue is Huimin (20s) memory of Iheon (20s) where he talks about fate and covering up the truth also the last panel of chapter 29.