Love Potion Blood Boy

Akihiro Hasumi has a fair complexion and a secret: an ancestor of his was a vampire. One day, he's drinking at home with Kazutaka, a guy he's been friends with since they were kids, gets drunk and gives away his secret. As a die-hard occult enthusiast, Kazutaka is dying to see if Akihiro can turn into a scary vampire and begs him to drink his blood. Akihiro grudgingly obliges... and a little bite is all it takes to make him start to feel funny... dreamy-eyed... and excited...

(Source: Renta!)