Collar (首輪, Kubiwa) is a device used by the DWMA on their Witch captives to coerce their assistance.[1]
Overview
The Collar appears as its namesake: a collar with studs on it as well as a skull mask to represent Death. The devices are bound to a Witch's neck and whenever a Witch begins to act out of DWMA's approval, the devices are set to somehow explode. Whether it is done automatically or via control is unknown. It's possible that the collars are unable to be conventionally removed.[1]