My Sister Is Out to Destroy the World

What do I do? I think my sister is plotting to destroy the world! Recently, my sweet and adorable sister suddenly became strangely irritable and violent. According to my investigations, not only has my sister become involved in a murder, she is also possessed by a witch from a thousand years ago! Now, my sister seems to be plotting to destroy the world! What’s worse, my sister is trying to pin the blame on me. She even told me that the food in prison is delicious and that there is good company in there! What am I supposed to do as an ordinary person?!