So, here we have a woman that is just naturally erotic and even has a somewhat logical reason for being an M. That isn't due to some over the top angst. AND she's not forcing the mc, but rather seducing him with her natural charms to try something he isn't too comfortable with (initially). She is pretty much wife material incarnate. Hell, she even seems like she would be an amazing mother. So top that off with the fact she is kinky? It's not even a competition.
The only thing that sucks about this, is because since she is clearly the best female character in this story, she will lose in the end. Japan seems to never disappoint on the front, lol. Hah, I made myself sad now.
Nothing bad happened. Actually, nothing happened at all. While other girls got better, Sayuki remains the same after 8 volumes. You've learned almost everything you need to know about her in this chapter
I don't like to dominate girl at all(and also I don't like to be dominated) but I love senpai/onee san type of girl and gotta admit that she is hella fucking cute