The protagonist, Sugita Yuuma, wakes up in an unfamiliar dark room and finds out that his classmate and crush, Jinmuji Miyu, is also trapped with him. They are then greeted by a masked Mistress who gives them a task to complete in order to escape. The first task is to fill a container with liquid in order to unlock the door, but there is no obvious water source. Miyu suggests using urine, but the container is too large for one person to fill. Yuuma ends up supporting Miyu as she fills the container, and they successfully complete the task. They wonder why they were put in this situation and who the Mistress really is.