Alr so if you want a detailed spoiler regarding chaewoo here it is:
(Warning:it is really long sorry)
First of all don't trust the narrator in this story at all
Sejin's mental health is badly deteriorated to the point where one have to ponder what to trust and what not,he has made many scenarios in his head and one of them includes his delusion that he is slow poisoning chaewoo
Which he is not
And of course chaewoo found out long before and was just putting up an act as he was suspicious of sejin
So he staged an act of suddenly collapsing to see sejin's reaction and that gave it away and he cursed my poor baby that may you always live in your pathetic delusions and die
You might find me heavily biased towards sejin but he is a victim through and through
Of course other singers are victims of this cruelty as well but sejin had it worst!!!!
Chaewoo was treated as a God in the club, everyone worshipped him and he secretly loved it
He never saw his followers more that pathetic and pitiful pawns
As you might There was the club rule of punishing singers by putting them in punishment room
And most singers who went there committed suicide or became very tame
Sejin as a child went there more than once
And was a victim of child abuse and sexual exploitation too in addition to the abuse of other singers
As a result he became mentally unstable and started having delusions of worms crawling on his skin so that bastard Kang Giha made him addicted to drugs knowing it will destroy him eventually
He became the person he is today and other people avoided him like a plague
So he became a loner and lunatic among singers.
The infuriating thing is that the night sejin was outside chaewoo's house in search for his brother,chaewoo actually heard him
Now there are some really big spoilers
There are three types of healers
The one who can only heal
One who can both heal and kill
And one who can only kill
And in addition there is a perfect healer who can even revive the dead but he is among the mentioned above healers and the research is still incomplete
So here's us the thing
Chaewoo is not a healer who can both kill and heal as everyone assumed him to
The night he was found covered in blood was because sejin's brother went to chaewoo's house and smashed everyone's head there
And the doctors who were killed
Well that was because of sejin but no one noticed
Chaewoo is not the kind person everyone thinks he is
When sejin was being interrogated,chaewoo was listening everything and praying that the man take sejin mistaking him to be chaewoo and he gets saved and when they actually took
Him he felt relieved but that was short term because sejin snitched on him too.
He hated sejin but he did not hate his situation.I mean he was treated as a sacred being,was never punished as others and had more right than others.He though of himself as superior of others, someone deserving of this
And when he saw sejin treated like shit he actually felt joy.
But .... Chaewoo started noticing long before that sejin might be a healer too
But it was just that he noticed it on his own and never told anyone
I mean why would he when he was being treated like a God.
He thought this place was originally only his,and some one like sejin did not deserve it at all,he was afraid of losing his importance and position
But now that when things went awry(sejin escaped,got chip remove cuz of yesak)
He in a fit of jealousy went to the boss and said he would tell him about a new and more powerful hero and gave sejin's location to his psycho of a brother who had romantic feelings for his own little brother and as you know is literally crazy
Aghh he ruined everything cuz of his jealousy and inferiority complex
If you think of sejin as a bad person
Remember that he was forced to be mentally unwell and so he isolated himself from the society.His actions are because of the same reason and many of them are just delusions my baby us having imagine the feeling and pain to seeing and feeling bugs on your skin,in your brain and your food, seeing himself as a fat and ugly person in the mirror
And harming himself without even realizing ( yeah I mentioned to forget when drugs effect was wearing off he found burn marks in his body and cut marks on his wrists which he did under the effects of drugs and delusions without even realizing) and now it's hard for him to decipher what's real and fake...
Where's chaewoo was the cause of his misfortune (I mean he was captured in the first place bcz he went to his house whilst looking for his psycho brother)and even other than that all that assault that was afflicted on him after that and chaewoo being just a buy stander so he can have it all and now when things aren't going his way he snitched on him to free himself
Ahhh what a long rant lol but yeah these are the spoilers

Ughhh I fucking hate chaewoo!!!!
That double faced bastard
(Coming from someone who has read the novel