More like a murder mystery.

So there is this weird plot hole in Opera Omnia.

To make things both short and simple, in Act 3 Sephiroth stumbled across the silt that corrupted him further and got him onto fight with Cloud and others. The same thing with silt happened to Caius, Hope, Snow, Jecht, Ultimecia and Emperor Matheus. And unlike Caius, Hope, Snow and Jecht who snapped out of it, Ultimecia and Matheus died in fight only to be brought back as a "shield" of Cloud of Darkness- alongside Sephiroth himself.

So there is this part I don't understand. They fought Sephiroth (as his Safer form) and he survived. Not only that, he seem to be snapped out of it like Caius did, but then he disappeared until the very end, being under Cloud of Darkness control. It was never implied why and how did this happened since again, he was never brought once as a topic by any character (excluding in Reno's arc where Kefka went to find Sephiroth to ruin whatever plan he had).

There is no way Sephiroth just stood there and let Cloud of Darkness use him as her shield only for her to destroy everything in his sight, even him. To make matters even weird, Sephiroth's behavior changed as well. Unlike at the end of Act 2 where he actually has a hope for fulfilling his own desires, by the end of Act 3 (before he dies yet again. On screen this time.) he is entirely hopeless, clearly giving up on everything.

So off screen, Sephiroth either:

a) succumbed due to his wounds after the fight,

b) got killed by something or someone,

c) took his own life.

It is just weird to me that this detail was left out.

(I also hope this ain't gonna end up on Pinterest or Pixiv or anywhere else behind my back. It would probably ruin a surprise. And altho till now he was mostly depicted either alive or fiant durring this goretober, he is pretty much dead here... but don't worry, his story does not end on Act 3 OR 4, heh.)