I think Sangwoo is trying to make Bum participate because he wants someone to share guilt with. I guess he also trying to trap Bum even more with this excuse, 'you killed now stay with me.'
I also believe Sangwoo had sex with her in front of Bum because he is an @sshole and he's having fun tormenting Bums feelings.
Sangwoo does seem like he's justified with killing the people he has killed....
DANGwoo!!!!!!
1. Yes, that seems to be part of his reason. If they are equally guilty then bum will never leave him
2.it was part of his plan to anger bum so he will have a reason to kill her.( Also, it's a way for koogi to show how twisted sangwoo is)
3. He wanted bum to enjoy killing as much as he did; it was another way to tie bum to his side. Rather than rage turning him on, it's more likely he is turned on by seeing other's in terrible pain which is a trait of someone who is sadistic.
4. Well, he is a serial killer. He would have justified his killings by making it so that the victims are at fault.
This is my own interpretation and I may be wrong.
I think Sangwoo wanted Bum to find pleasure or comfort from killing Jieun. Sangwoo wanted Bum to take the initiative to kill so he carefully selected who he thought would be the perfect person, Jieun. Sangwoo probably thought Jieun's strong personality along with his friend's teasing would be enough to enrage Bum to kill Jieun. He had sex with her to take advantage of Bum's jealously as a last effort to make Bum mad. Sangwoo's efforts were really a failure. Yes Bum did kill Jieun on his own but it wasn't because of her personality. In the heat of the moment, Bum wasn't thinking about Jieun, to him he was killing his classmate. Rather than Jieun because he was a bitch, he killed her because he was triggered. Sangwoo seemed happy that Bum had released his anger and I think he wanted Bum to express some sort of satisfaction for his "accomplishment". Instead Bum was shocked by what happened and feels guilty for his action.
Not sure if Sangwoo really blames Bum for all the killings or if he just said that to make Bum feel more obligated to stay. Maybe he wants Bum to accept the killings and to tell he's been a participant in all of the killings since the begining (even though that's not really true).
Sangwoo does have a reason for killing, we just don't know what it is yet (something connected to his parents?). I've always felt that Sangwoo kept Bum around because he saw him as his favorite toy. I don't think he really cares about Bum as long as he stays entertained.
Questions with spoilers!!!
I'm a bit confused about killing stalking. so could someone that has already read the chapter 20 make me understand more?
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1) Sangwoo is trying to make bum participate of his murders. maybe is it because he wants bum to be a killer too, since he seems to show some kind of interest on him?
2) I really didn't understand why sangwoo has to fuck her in front of bum. couldn't it be better only killing her, like that old man? what's with that scene and it's meaning?
3) Sangwoo was sooo mad with bum. I know he was hoping bum to "love(?)" killing people, but... he blames bum for a lot of things. Is it because of bum's reaction? Anyway, he seems act angry with him since before. It's like this rage makes him turned-on.
4) Sometimes sangwoo acts like making justice (at leat in his thought). Am I right?
Σ(っ°Д °;)っI'm sooo sorry for making these questions. If a pure hearted person explain me the context I would be grateful. >.<