Haven't seen yet apart from Omni's blog pics, but from the viewpoint of a person who's going into the anime without the game (yeah right) with a bit of inferencing from what they show:
Spoiler:
1. The Black Knights call them Fragments
-> usually means that whatever pulls them into the Red Night is linked to them.
2. Girl in crystal
-> Centerpoint of Red Night.
3. Red Night is random
-> Power is unstable
So, following logic, that girl is the cause of Red Night, and somehow needs their 'fragments'.
Note trope:
Nice Job Breaking It Hero
Possibility that the girl is a Big Bad exists.
Story-wise, what do you think this will focus on more? The backstory (Red Night and why) or the girls' story (Misuzu, Yukiko, Shiori, stalker-girl)?