新妹魔王の契約者 新妹魔王的契約者 新妹魔王的契约者 The_Testament_of_Sister_New_Devil
The Testament of Sister New Devil (新妹魔王の契約者『テスタメント』), also known as Shinmai Maou no Keiyakusha, is a Light Novel written by Uesu Tetsuto and illustrated by Ookuma Nekosuke (Nitro+) released since September 2012.
It has 2 manga adaptations and an anime adaptation.