Episode 17 (technically 18):
This episode kind of explained to me the point of episode 0. I guess it was used to not break the pacing too badly. But... It was still broken. A flashback would have worked just as well, and it would not make things better considering how abrupt the ending felt, and how it did not explain a few inconsistencies in the last episode itself. It can be that this was the whole point, though. Still I prefer the yuri ending, it just felt way better.
overall, I am still a bit conflicted. The show has a very slow and confusing start, had a few great moments, but also a few where the story-telling felt jumbled, as if important things were cut. Perhaps making it a 24 episodes series with a bit more foreshadowing and/or mystery in the first half would have worked better.