Something that always bugs me about this manhwa (and a lot of other yuri manhwas) is that when they're having sex, it's so one sided. Sori's always like "I can't hold back anymore", and then she doesn't get any.
I don't think the author has a very good understanding of lesbians. That's not how it works.
I mean, yeah the top is usually the one who takes the lead, but it doesn't mean that the bottom is supposed to just lay there and not do anything.