Cursed friendship

Vampire! A scream echoes through the village another victim. You have enough, and now you're searching for a answer to get somehow rid of that thing. You leave the village and wander to an abandoned church. It was planned to be for Apollo the Patron Saint of the village, but something went wrong as it belongs to Apollyon the demon. You have no other choice and still enter. A mistake. As Apollyon cursed you with immortality. And to top that, as you confront the Vampire. It turns out they don't want to bite people but they need to survive. They want a friend. Yes no joke. Well you are immortal now, you could offer your blood, So that the villagers are safe.