My Scary Girl (2006)

Dae-Woo, a man with no experience in the art of relationships, is encouraged by his friend to ask Lee Mina, the girl who's just moved in downstairs, out on a date. Unexpectedly successful, he falls in love. When Lee Mina's ex-boyfriend shows up and ruins the new relationship, she takes matters into her own hands. A distraught Dae-Woo begins investigating Lee Mina's murky past and discovers a series of scary secrets.