How does the tadpole even survive in him..
This is the question that gets overlooked the most. Why would a tadpole ever enter a dead body?
This whole vampire story seems so out of place with everything else that is happening. They just wanted a vampire companion because someone thinks vampires are cool and forced it in.
For me, this is a really watered down version of a vampire slapped on top of an already complicated plot. They should have shown restraint and waited for an opportunity to tell a proper vampire story later in the game.