The Pain in My Neck

Recently something's really been doing a number on Sumin. No medical test can seem to tell what it is, though. After several unsuccessful checkups, Sumin walks home to find... his next-door neighbor drinking the blood of a random stranger! Sumin's thoroughly creeped out, but he soon becomes interested when the vampire claims that he can suck all of Sumin's pain away. What could possibly go wrong? It'll be worth it if a small pain in his neck will rid him of this mysterious ailment, right? Right?

(Source: Lezhin Comics)