The recent Manhwa Awards nominations got me thinking about this and, I'm ready to accept that Rachel is just a heartless @#$@%.
We can't really be sure yet, I think, but with what she did with Baam and how she tried to play Koon and the others she is a sociopath.
My feeling is that she has a more complex motivation behind her actions but in the end what she's done speaks for itself. Nobody lured her into the tower. Nobody forced her to make a deals with the devils to climb it either. There is nothing inherently wrong with her dream of seeing the stars but what defines a person is not a dream but what they are willing to do to achieve it. That's when we found out who she really was, IMO.
Even now, it's all someone else's fault in her mind; and that's even more telling. She under the delusion that she hasn't done anything wrong; and we know, as should she, that's not true. That's the thing about her I really dislike more than anything. The self deception. When I compare her to my favorite ToG character Androssi, who is also a monster of sorts, self awareness is a huge difference.
A part of my favorite quote from her goes like this....
"I really don't know any other way than this.
I'm not expecting you to understand me though, and it doesn't change the fact that I'm a devil either. But I'm just following what my heart tells me to do. Isn't it the same for everyone? Only, we weren't wishing for the same thing."
Rachel could never say something like this because isn't willing to take responsibility for her own actions. When Androssi has done something terrible she sees it for what it is and makes no excuses. She'll do what she wants, and make no apologies for it, but she won't pretend it's not bad. The strong eat the weak, and she's strong. That's the world she knows, and thrives in, and she knows that's wrong.
Rachel doesn't accept that hurting others to pursue her goals is wrong and that makes here a far worse person in my eyes.