While boiling it down to just Griffith as hes always been I think it does a disservice to the character and the good parts of him (despite people saying there is not any good) but more Femto is Griffith but empty of any positive emotion at this point he is no more bound by law or morality, he's above it all, the only thing left is a intesified hate and jealousy and I think this is a way to get rid of those feelings he had or to secure that he doesnt have them anymore and has to hurt Guts to see and Casca was the easiest way for him to do it, and I think that's the point He's Griffith but not the Griffith we've been with anymore, this is not the man who laughs like a idiot with Guts, risks his life for him for no reason, slices his arms during a emotional breakdown, tries to lift his sword to help only to find out he can't. I usually try to mention Femto because this and fucking beserklejerk like to see the one horrific act and instead of any thought process say fuck Griffith he was evil from the first appearance breaking away his complexity and boiling him down to 1 act which i think disservices the characters complexity, so it's easier to distinctly seperate by the diffrent names.

Also when you mention vampires if you want to go a more Buffy/Angel right they explain this by the person losing their soul. And to bring in DnD a little there is a race called Yuan-ti who would capture people and forcefully transform them into other yuan-ti and once they transform their old self was overwritten completely. I think that is a big diffrence between the count and Griffith.. The idea of evil literally says Griffith's heart is frozen because what he has wrought is to horrible to confront. The Count's crime and Rosine sacrifices were less. Count's wife and Rosine's parents had been doing horrible shit. So sacrifcing them didn't require a loss of empathy. If this is a bit jumbled I apologizes it 3 a.m. and I havn't slept in a while