Peak. I came in for 『AURA MONSTER』but left with more than I bargained for. 100000/10 for me. Onto theory crafting.
I feel like Subaru has lapses in memory, which would be the only explanation for what happened between him and Meili. Now, in those lapses he probably tweaks out or something.
Onto what happened in the STAIRS loop, Shaula probably got killed while trying to kill the people in the tower. It isn't insane to imagine that maybe Emilia and Beatrice as well as the others did enough damage to kill her but Shaula also got most of them down before she died.
Right before he died on the balcony, the black smoke seems to have some sort of ability to cut. I can only surmise this to be Satella's shadows or something because nothing we've seen so far can do this. Maybe the Black Serpent from the Emilia backstory OVA, but that thing melts you from the point it touched you. Also it doesn't have any tentacles to be the black serpent.
The more interesting part is what happened right before he died. There is no way in hell Rem just got back up and killed Subaru. So, I have 2 possible theories as to what happened. Capella, The Sin Archbishop of Lust. Or Rui Arneb, the Sin Archbishop of Gluttony.
Capella seems like a stretch for me because she isn't really mentioned or even shown in the opening, so she is probably not the person.
But Rui Arneb? She seems the most likely person. As we've seen in the S3 finale, Rui can shape shift into people. Presumably it is people that the trio (Rui, Lye and Roy) have eaten. So, that would explain how she came in Rem's Visage. Next, it seemed like she knew about RBD as she hinted at it. And that can only happen if Subaru had his memories taken, WHICH IS WHAT HAPPENED! So, that leaves me with the conclusion that that person is Rui Arneb or at least the other Archbishops of Gluttony.
[CONTINUED IN THE REPLIES]