Hellsing, Owari no Seraph Recommendations
Both are focused on an organization that fights against vampires.
-The second main character from both series (aka Seras and Mika) are forced to become part-vampires who at first refuse to drink blood.
-Organizations that fight against vampires.
-Both the main characters are shown to be terribly strong; some might even say overpowered.
-The weapons the characters use are specially designed to be used against vampires.