High School DxD Vol. 1 (light novel)

I'm going to make this school my harem!
When a cute girl asks Issei out, he believes his twisted fantasies are finally coming true. Too bad the girl sprouts a pair of black wings and stabs him with a spear on their first date! Saved by his school's number one beauty, Rias Gremory, Issei is transformed into a demon and made her servant. Issei hopes to rise through the ranks of demonkind to grow powerful enough to create his harem, but in a city with fallen angels and insane priests, he'll be lucky if he can live long enough to do it!