Thirst (2009 movie)

Thirst is a 2009 horror/drama movie. It was written and directed by Park Chan-wook. It tells the story of a priest who is in love with his friend's wife turning into a vampire through a failed medical experiment. Park said, “this film was originally called "The Bat" to convey a sense of horror."
Plot.
Sang-hyun, a priest, is helping in a program for developing vaccines, which takes place in a hospital in an another country. He died during the experiments after becoming infected with a virus. However, after receiving an unidentified blood transfusion, he came back to life. However, the blood changed him into Vampire.
After this, many people became his followers, because they believed that he could perform miracles. Sang-hyun feels irresistible desire for Tae-ju, the wife of his friend and follow. Tae-ju also becomes attracted to Sang-hyun. Falling in love with Tae-ju, Sang-hyun abandons his life as a priest, falls into the world of Tae-ju.
The more they love, the more they are at risk. After finding out that Sang-hyun is a Vampire, Tae-ju tries to avoid him. However, eventually she asks Sang-hyun to kill her husband, Kang-woo. Sang-hyun tries to avoid killing Kang-woo, but eventually decides to kill him for Tae-ju and accepts her proposal.