There’s been a lot of speculation on how Subaru lost his memories. Based on Eps. 74, 75, and 76 with amnesiac Subaru remembering “Memories are what shape a person.” which was said by Rui in Ep. 74 at 19:26, potentially hinting at her having possessed Subaru, his blacking out and waking up around a bunch of dead mabeasts he hadn’t killed himself and waking up having strangled Meili to death in Ep. 75, and Meili’s memories of what happened two days ago in Ep. 76, I believe this points to Subaru being possessed, but how did Rui (and potentially Lye and Roy) enter the tower given Shaula can detect who has left the tower since she knew amnesiac Subaru had left and given her prior warning that challengers to the tower cannot leave, which perhaps indicates she can sense how many challengers to the Pleiades Watchtower there are? Which means it may not be as simple as the Gluttony trio coming straight through the entrance even though the distortion and Sand Time had been dispelled.
“Memories are what shape a person.” may point to a second meaning in that those memories have been eaten can be claimed/possessed by Gluttony wielders. Perhaps reading the Book of the Dead of someone whose memories had been eaten by the Authority of Gluttony can result in a Sin Archbishop of Gluttony emerging to use his/her Authority against you, and that may be how Subaru lost his memories, ’cause they’d been eaten due to that deceased person’s memories being that Sin Archbishop of Gluttony’s possession, so Subaru likely read the Book of the Dead of someone tied to Rui, Lye, or Roy or perhaps even a previous Sin Archbishop of Gluttony (although I doubt this), and then the Gluttony wielder seized control of the recollection of the memories, using the Authority of Gluttony on Subaru. And I’m referring only to those who have had their memories eaten, not those who had both their name and memories eaten, leading to them being erased from the world. I know Rem appeared to be possessed in Ep. 74, but I have no idea what could explain aside from Rui teleporting from wherever she had been in during Season 3 before switching places with Lye in Ep. 66 when she swapped with Lye in the form of the green-haired woman (man?).
That’d be why Subaru had been reading many Books of the Dead and was normal when he interrupted Meili searching for Elsa’s Book of the Dead, and then when Meili returned, he was no longer himself as his memories had already been eaten, which is why he said that Meili’s face looks full of flavour, a very Gluttonyesque thing to say. It may not have been amnesiac Subaru, but the old Subaru should already have been gone at that point, which is why Meili thought to ask him about whether she could hold him to what he said last night in Ep. 75. This’d explain how Shaula, with her very keen sense of smell, didn’t smell other beings with high levels of miasma inside the tower aside from Subaru, and it’s that the Authority of Gluttony can be used when one is reading a Book of the Dead. Given Subaru by himself already emits a ton of miasma, Shaula may not have been able to detect a discernible difference unless she were really close by given miasma levels dissipate over distance like any other gas as shown by Ep. 69 by the ever increasing amounts of miasma as the group got closer and closer to the source of the miasma, not to mention she may have already retired for the night.
Feel free to share your thoughts on this.
