Ookami ga Dekita Hi 1992

Taihei's difficult days are just beginning. His girlfriend Natsuko has a sister called Kanoko who falls victim to a a disease that has afflicted women of the family for generations, causing a sudden eruption of hair across her body. When she turns into a wolf and escapes into the woods, Taihei and Natsuko come after her and stumble across an unidentified body. The police claim the wolf is to blame. This begins a frantic chase where the myth of the werewolf and Japanese folklore blend together.