Curse is an instrumental background song in the anime xxxHolic. It was written and composed especially for the anime.
Curse has a mysterious and sinister feeling to it. This is because it is played at times when Watanuki notices something strange going on that he cannot really explain. The song is played to enhance the feeling of mystery and suspense and it sometimes makes situations more creepy and scary. For example, this song was played when Watanuki saw that a girl in his school was mysteriously growing what looked like angel wings and that her attitude was also changing.