[Weird recovery] + [No system] + [Crazy male protagonist] + [Decisive killing] + [No female protagonist] + [Cthulhu] The dark prison merges with reality, and strange creatures invade the world through the 'door' .
An organization was quietly born, and they called themselves the Prison Keepers. They keep weird things out of the 'door' and capture and contain weird creatures that come into the world.
Lu Xiao accidentally fell into the dark prison and lived alone in the dark prison for three years. After being discovered by the Prisoner organization, Lu Xiao later became an S-class protected object in the Prisoner organization.