Azure Night, Waltz of Rapture

When a night out to a piano recital turns into a literal nightmare for Seoyoon, she's unceremoniously inducted into a world of horrifying beings. There, she meets Heewon, a charming "superbia" who informs her that she is nothing more than food for these creatures born of sin. Now, she must succumb to the likes of vampires and incubi as they feed on her for sustenance. Can she escape the darkness that lurks under the cover of night, or will she find a reason to stay inside this sinister realm? Adapted from a web novel of the same name