Re:Zero kara Hajimeru Isekai Seikatsu 2nd Season Part 2 Episode 12 Discussion

mozgow said:
First, the ending of arc 4 (there's a high probability it will be in a director's cut version, if they make one).
The last scene for arc 4 in the LN describes someone waking up in some "room" similar to the tomb. At first it's only hinted but soon it's confirmed it's actually Echidna who took over Ryuzu Shima's body. After complaining she did not feel anything for being alive again (after 400 years), she renames herself as Omega and walks in into the forest. It is also mentioned she has the other Witches souls with her. The last line in the volume is "The Witch has returned".

mozgow said:
Second, about Echidna.
In the LN both Roswaal and Beatrice confirm that Echidna inside the tomb is the one they knew 400 years ago, and they do not know why the one Subaru and Emilia met looked differently.

mozgow said:
In the spoiler below is my theory why is it that, based on other skipped content from the LN.
The tea party Echidna does not have all memories and personality traits of the tomb Echidna.

When Subaru was talking with Ryuzu about Sanctuary's past, she told him that the experiments failed because the vessels (Ryuzu copies) were too small for Echidna's soul. When Echidna tried to use those vessels anyway, it ended pretty badly. The last time she tried it was two generations ago and it ended with the failed copy going berserk, since it had enough of original Echidna power, but not enough of her knowledge. The young lady Ros from two generations ago had to deal with it, most likely killing it and destroying part of Echidna's soul in the process.

We do not know how many times Echidna tried to pour her soul into those vessels, but I assume it was at least a dozen of times (if not more). After each failure part of her soul was destroyed too.

Then why she look different? I think she changed her looks to match what she remembered and knew about herself.

I think we will eventually learn what was the cause, but for now this is my leading theory.

mozgow said:
Oh, and if you've read about Omega, you might want to read this too (separate spoiler, just to be safe).
If Ryuzu copies were too small to hold Echidna's soul, how was she able to posses Ryuzu Shima?

Well, from Subaru memories she learnt about data compression and applied this concept to her soul xD

mozgow said:
Third, about Beatrice's contract with Subaru.
After forming the contract Beatrice explains to Subaru that she can't produce mana by herself and that she must drain it from others. When she was in the Library, she drained mana from whoever was in the Mansion. But now, that she formed contract with Subaru, she can drain mana only from him. And since Subaru's gate is broken, she can't get much mana from him.

Then Subaru asks how much mana does she have left and Beatrice says she used all her mana to cast Al Shamak.

It means Beatrice's knowledge about spells will be useless for a while, since she won't have enough mana to cast them. But with enough time she can drain enough mana to cast some of them again.