Sisterly love - and guilt to a degree. But a guilt most of us have never experienced in a sibling relationship. If your parents get murdered when you are young ... that will leave quite the scars. And it is exactly what happens here - it's how the movie begins quite frankly. From there we jump forward and see the girls who have grown up, but never fully overcame what happened ... can you blame them? One might or seems to have less issues than the other and there might be a reason for that.
Now there are many things that might make this true and the movie keeps you guessing, especially when it blurs line between reality and what the main character(s) see! I am not used to seeing a German thriller movie that works quite as well - is something I am used hearing and I have said it before too. But recent years have shown to those who doubt the quality (or maybe are just plain fed up with all the comedies and dramas and lack of good genre content) ... that they shouldn't! And this movie is another very fine example of that ...
Now there are many things that might make this true and the movie keeps you guessing, especially when it blurs line between reality and what the main character(s) see! I am not used to seeing a German thriller movie that works quite as well - is something I am used hearing and I have said it before too. But recent years have shown to those who doubt the quality (or maybe are just plain fed up with all the comedies and dramas and lack of good genre content) ... that they shouldn't! And this movie is another very fine example of that ...