Then what do you think vampirism really is?
I'm not sure but I think it must be connected to Christianity to make sense because of historical accounts, in the orthodox church there are some documents made by church fathers but I didn't investigate enough yet.
Something like lifestyle rather than occult practices.
And there must be esoteric component, because there are many variations of vampirism I think not all are a thing.
There's a lot to peruse for philosophical, sociological or esoteric biting
Yes, however that bite is to be defined it must drastically transform the one being bitten IMO, either to enlightenment (positive) or curse (negative), otherwise there is no essence.
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My perception might be wrong but drinking blood or energy vampire just doesn't sound like a real thing.
Biggest issue is that there are 2 kinds of vampirisms, one according to old folklore beliefs and other according to modern beliefs started sometime with aristocracy.
And there doesn't seem to be any connection of the 2.