Spirit Pacts
The first vampire or vampires were beings that made pacts with powerful spirits for immortality, this means that the beast is a piece of this great spirit or set of spirits and the thirst is a blood offering that must be made through imbibing it to keep the immortality and the other various boons the spirits offer. The clan weaknesses are just what happens when you deal with malicious spirits, you take on aspects of them.

The War For Nod
The antediluvians cursed eachother. This began with simple slights, Lasombra being unable to see their reflection because...