Puella Magi Oriko Magica: Sadness Prayer Vol. 2 (manga)

Oriko sees her use of Kiriko as an attack dog against other magical girls as a justifiable means to achieving a greater purpose--protecting the world from the destructive force of Walpurgisnacht. However, their arrangement has piqued the interest of another magical girl, who has her own reasons for wanting a magical killer like Kiriko at her beck and call...Will her savory offer sway Kiriko's allegiance and leave Oriko herself open to attack?!