Board Thread:Questions and Answers/@comment-27279375-20160303041647/@comment-25121259-20160303215054

This remains unexplained, though it is kind of Ragna's hallmark at this point, I mean he lost his memories like 3-4 times already (and that is counting only the current line) ?

This might have something to do with Izanami awakening the Beast at the end of CP, seeing as at the end of the Dark War, when the Black Beast's Body reverted back to a human form, it was without any memories, on the other hand, Ragna did retain his memories at the end of his bad CS ending...

Either way, it is alluded that it is thanks to Amaterasu that Ragna is within the Embryo and keeps on existing (since he actually should either continue his metamorphosis (essentially his CS bad ending) or turn into Seithr like the rest of those that are not among the Entitled).

Also, seeing how many parallels there are between Ragna and Naoto, I wouldn't be surprised if he also lost his memories (having them only to a certain point), especially when Valk/Nine and Izanami point to different places that he came from.