"A Harrowing Affair" is an original Megurine Luka song. It was created to celebrate Halloween and was released as a single.
The song is about a rich family who burned down the house of another family in order to acquire their land. Klein, the child survives and the rich family took him in to become their slave. However, he is unaware that the rich family was the one responsible for his parents' death. Ten years later, while looking at a picture that he kept with him since he was taken captive (presumably a picture of his family), Melody grabs it, tore it into pieces, threw them into a fireplace, and harshly told him to stop living in a dream. In an instant, Klein learns the truth behind his parents' death. So when night arrived, he finally carried out his revenge by burning down the rich family's house.