Ah, yuri genre truly has so many masterpieces!
Summary: Sato did nothing wrong. Her "friend" was never her friend at all. She wavered when she seen Sato's aunt. And when she discovered the truth instead of trying to reason with Sato (though I admit, it is a dumb idea, but she most likely wouldn't die in that scenario), the first thing to do for her is to sneakly take a picture and sell her friend to someone, ultimately dooming her entire "castle".
That being said, despite I , to some degree , admire Sato, its better to stay away from her, the farthest the better.
Great story with alot of controversial points and usage of gray to black morale spectrum.
I even started to doubt if it is really that good to be completely sane and rational. The characters are fucked, but when it comes to love , their devition is something... Don't know, inspiring? I don't think this is the right word.
Compared to that love , real life love is somehow down to earth, pragmatic and banal. Sterile. (Unless you are unexperienced teenager). It is almost like the "imaginary" love is real and the "real" one is fake.