Responses
I was wrong about my prediction of our first time watching Guwon act inexcusably cruel would be him brutally getting rid of the zombified sick child along with his "enablers". I'm 100% sure Guwon didn't kill Teach's father but he might carelessly admit he could've saved him but chose not to. I see the whole thing going down exactly how you describe it, Teach probably did whack his dad in self defense.
Now I definitely can see Guwon watching his father get killed and not stepping thinking it's a kill he don't have to do and admits that.
Some of my thoughts and pieces
In Chapter 0-1 Guwon kills that man wacks him in the head. That's the same man Teach is saying is his father but honestly I think Teach is losing it right here. Hallucinating.
Because that man that was killed by Guwon clearly told Teach "Look what we found I'll make sure you have a painless death" when he found Teach injured on the ground.
Unless Teach hallucinated those words and it was dad and Guwon killed his father seeing him as no use this is gonna be so fucked.
But honestly I think it's the other way around. Because someone was screaming "please don't kill me, take whatever you want, some one is trying to rob us please help!" Which one can assume that person got killed after that. (I think it was Teachs Dad) They were defending against someone because teach was wounded.
That robber guy killed the man pleading with him then started to loot the place found Teach said he'll give him a painless death and got wacked by Guwon that's the same man Doctor and Teach found dead in that house.
But maybe something else happened. I think prior to that situation when Guwon found Teach.
Because Teach was found injured on the ground by both men. The looter and Guwon.
So unless Teach and his dad fell out before hand and his dad injured him in the head and he fought back and killed him and now he has triggers because his dad hit him the same way Guwon killed that man hence why he has those dreams of that exact killing stance over him and always wakes up trying to defend himself. But his mind can't accept the betrayal from his dad and the fact he killed his dad in defense.
Or why he probably thinks Guwon killed his dad since Guwon stance was the same when he killed that man.
Or maybe he killed his dad a while ago and bandaged his head and in his distraught state went back to his home and passed out there and then boom intro the scene of everything we know
The author definitely trying to keep us confused and unsure fo sure.
But I vote Teach killed his dad and his mind just can’t accept that.