Finished it about an hour or two ago, and...wow.
I was very, very surprised by the plot twist. Very surprised. It was just...wow. I did not see that one coming. The MC being a yandere just never occurred to me. Nice job.
I think it would have been a little more impactful if the stepbrother hadn't tricked her into killing the girlfriend. Then, at the end, instead of killing him out of anger, she could have killed him because he knew her secret. This would mean that the MC would have been the only one in the wrong, and the stepbrother that the story was pointing to would have done nothing bad at all. Instead, the person the story had been saying was evil turned out to be, in fact, evil. Not a big surprise for me.
Also, I didn't really like how the MC speaking and the MC's inner thoughts both had her pic on the side and her name on the top. That made it hard to tell when she was talking and when she was inner monologuing, except when common sense ruled that she couldn't have said that out loud. Perhaps you could have put her thoughts in italics, or you could have taken away her name thing and pic for her inner thoughts.
Didn't really like the gratuitous cursing either. Just saying.
Overall, while the presentation could have been a little better, you guys did a great job with the game. Hoping to see more great things from you guys in the future!