The Scholar Who Walks the Night
밤을 걷는 선비 (original)
When Jo Yang Sun is driven out of house and home after her father is framed for a crime, she is forced to crossdress in order to make ends meet as a bookseller, where she meets Kim Sung Yeol, a handsome, but mysterious scholar who is actually a vampire. Meanwhile, an evil presence at the royal palace stops at nothing to keep the Crown Prince from claiming his rightful throne.
Starring Lee Joon-gi, Lee Yu-bi, Max Changmin, Lee Soo-hyuk, Kim So-eun, Jang Hee-jin, Lee Soon-jae, Choi Tae-hwan, Park So Young, Moo Jin-sung
Watch "The Scholar Who Walks the Night" on Rakuten Viki released in 2015. It's a drama show, and has a rating of 7.2 out of 10 from Imdb which is usually fine for this kind of show, and is currently available to watch for free.