I like it. Story is simple, and demo is short, but it's well put together and paced decently.
I would've liked more variety in what our antagonist thinks about her sister and why. For example, she could be nice to Mara because she thinks she's a devil and wants to be on her good side when killings start, or because she's genuinely nice and caring person. Or she could shun Mara because she think she's a devil, or because she's not strong enough to act against mob mentality and fears becoming the same shunned and hurt outcast Mara is.
Hope you'll write more, because this story deserves to be continued.