"Shadow Hour"), a period of time that exists between one day and the next.[12] During this time, most people turned into coffins and they are not aware of the Dark Hour; however, there is a select group of people who are.[12] The Dark Hour bends reality; Gekkoukan High School, where most of the characters attend school during the day, becomes a huge labyrinthine tower called Tartarus, and beasts known as Shadows roam the area, preying on the minds of those still conscious.[2] The Shadows leave their victims in near-catatonic states outside of the Dark Hour.[13] To investigate and learn about the Dark Hour, Shadows, and Tartarus, the "Specialized Extracurricular Execution Squad", or SEES, was created.