Highschool DxD/ Hellsing.
Plot: When Issei Hyoudou is killed by Raynare his fallen angel girlfriend Issei in his desire to live discards his humanity and becomes a vampire like Alucard from Hellsing.
Rules: Issei must not become a devil he must become a vampire and stay one.
Issei must also have had a bad childhood one that makes him hate humans but because he was so week he put on a mask of being a pervert in order to hide his hatred. His hatred must also extend to god who he likes to call the hypocrite god.
For this story you can give Issei a harem or keep him single.
Issei's powers should be exactly like Alucard's but he must have the ability to use any and all dark magic, as for a sacred gear you can give him boosted gear or any other gear that you want him to have.
Issei can interact and be allies with devils but he can't become one or be someones slave like Alucard was to Integra.
When Issei kills someone and drains their blood he gains their memories and powers no matter what species they are. (the only exception are the angels due to their holy aura)
Forbidden: No yoai.
Issei can not be killed off from the story.
No nice and kind Issei he's a vampire blood, murder, and sex is what it's all about.
No slave Issei he's his own master.
Issei can not be made weak in this story he must become stronge enough to over power any and all enemies that he will have.