Sisters Grimm

The twins are from the Grimm family. The Grimm family has been protecting humanity by hunting the supernatural for centuries through many generations. All this contact with the other realm has left them supernatural themselves. A secret the family must keep from the organization they founded otherwise they might turn from the hunters to the hunted. Fastforward to today. You are a new recruit to join BTD the organization founded by Grimm and you are being assigned and trained by the Grimm Twins Mary and Mourn.