Crackpot theory time.
Based on my recent playthrough of katalist i might have come to a basis of what svelva's role might be in the story. I think that Vaila might not be the originator of the "katalist" spell. Atleast on the alchemy theory of working with souls. We know according to ingame lore that:
Philtering is To Meddle with Souls. To avoid. Some minor versions of it involving spirit souls and minor familiars can be found in resonation recipes. Anything beyond that is mostly Prohibited by Law.
Is a existing form of alchemy. This shows that Vaila is dabbeling in some rather dangerous parts of alchemy when altering our body and soul. I believe that the energie residues of a person that you absorb is part of Soul Philtering . There is mention of another character who dabbles that field. That being Svelva.
North of the snow barren village there exists a tree who asks you if you are "one of svelva's" because you have succubus energy mixed with other souls in your body. It would make sense if svelva also is able to make a similar spell like the "katalist" spell since Si (the green agglomorate you meet in the old housing facility) Refers to you as " A brother and the same apple but from a different tree" What if Si and maby also bonnie (she used to have an agglomorate status in the code, and she also has an essence that according to when you meditate on it "doesnt exist") are the same kind of being but made by svelva. I think svelva is going to be one of the final antagonists in the game opposing Dilan who is working for vaila and the resistance.
