Responses
I don't think Sori is actually against it or that she doesn't like it. It's more like she noticed that Iseul was not enjoying and so she got scared and stopped.
I like to be rough as well, but if I noticed that the other person was not as into it as they told me to, I'd have stopped as well. If you're on top, you're in control - that means you gotta be able to tell if sth is wrong and stop immediately which is what Sori did.
One thing i learned from the later chapter is that, I may have been a little sadistic then T__T although my gf wanted to be choked as well, it's new to me how sori reacted. Sori is the definition of a softie top