Bizarre Detainment Facility: You're Containing a Human Like Me?

[No System] + [No Routine] + [No Female Protagonist] + [Cthulhu] + [Male Protagonist Crazy Criticism] (There is no pretentious plot, please proceed with caution!)
 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 the weird ones out of the "door" and capture and contain the 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.
 When he was discovered by the prison guard organization, he was already crazy! ! !