A town enveloped by twilight. This place without morning and noon is permanently bustling with people engrossed in their own activities. The only thing they fear is the night, the moment when everything is engulfed in darkness. ‘When night falls, the demons will take us to Hell.’ The coming of the night heralds the arrival of the demons. Their purpose is unknown, they kidnap and kill people for no apparent reason. To fight these demons, the people established The Special Security Guard, also known as Yonomori. The protagonist, Mahora, also belongs to Yonomori and is on a mission to defeat the demons. However, he is currently living with Shuu, a demon he is supposed to defeat. On the recommendation of the current commander, he and a group of problematic members of the guard are transferred to Special Division 3, which is tasked with defeating dangerous demons. One day during a mission, he is attacked by another demon who orders Mahora to return Shuu to him.