Baldur’s Gate 3 walkthrough is here. The hero needs to do Asterion companion quest, and there is a vampire hunter hunting the vampire. So defeat Grandel, and progress the companion quest.
The steps leading to and progressing for the rogue specialization class companion quest are as follows.
Meet Asterion after the Mind Flayer ship crashes.
Allow Asterion to creep up on the hero whilst the hero is sleeping, in order for Asterion to feed. This will get the hero the Bloodless trait.
Get to the Hag House. Outside the hag house, get to Grandel the vampire hunter.
Allow Asterion to do whatever he wants in the conversation options.
Baldur’s Gate 3 is 2023 Game of the Year.