Rias's Pet and Protector (Demogorgon and Highschool DxD)
Long ago fallen angels learned of a place called, "The Upsidedown" and learned about a beast named the Demogorgon. A deadly predator that can teleport from the Upsidedown to the real world at will to any place. The fallen figured that if they could control this beast then they will be able to finish off the devils onc...