What was the point of the dead fish?

I was under the impression that it made Mima realize someone was able to get into her room, and that her fish were killed as a sort of "revenge".

"I'm not reckless . . . I'm skillful!"

I interpreted it as a breaking point for her. Eventhough she started losing more and more of her old life (and her old self) she still had the little things to fall back on, like feeding her fish. This routine was what kept her sense of self, she was Mima who had fish and fed those fish, that's who she was, no matter what she did the rest of the day. When her fish died however she was confronted with the fact(/idea) that her old life was completely over; she couldn't simply keep on denying that she hated her new life.

I thought it was one of the emotional peaks of the movie, better than the rapescene itself.

You, in the boobs

Correct me if I'm wrong but the fish weren't really dead. I'm pretty sure there was a shot at the end of that scene of them swimming around again.

So I do agree it was a breaking point for her...a breaking point in her sense of reality or illusion. Something inside her had died or been sacrificed after doing that rape scene, and this or her guilt over that manifested in her seeing her fishies dead. But they weren't really dead.

I just rewatched it. Yeah at the end of that scene they show at least two fish still swimming around and no dead ones floating. I took it to mean she had imagined them dead.