go to the forest of the abandoned church and then go south of the church almost where you find the werewolf and interact with the corpse, a ghoul will start a fight and once you beat it a girl appears telling you she is looking for a vampire. go to the port town and talk with the ship owner to travel with the old lady that knows about vampires, she gives you the key to the ancient castle, there are a few side quest on the way but most are irrelevant and you can skip them, go to the camp for adventurers and talk to the girl in the bottom left part of the map and accept her quest, go to the temple of the serpent and kill the snake girl boss to get her blood and return to the girl in adventurers camp, now you can go to the abyssal woods depths, travel through the woods depths until you find the exit to the poison swamp and to the ancient castle, talk to the vampire girl and let her join your party, once she joins return to the Forest of the abandoned church and go where you found the death corpse and the ghoul for the first time and that's all.
Warning, once you complete the quest you will be unable to enter the bar in the royal capital or the low traffic street since there is a bug that triggers the last scenes of the quest again when you do.
