Dance in the Vampire Bund, High School DxD Recommendations
there both about the main character being a servant/underling to a powerful vampire and are both set around a high school.
dance in the vampire bund is a darker and more serious anime while the other one is a comedy.
Both involve supernatural elements, plot, "plot", and impossible love.
Highschool DxD is way more over the top when it comes to the fanservice.