Guromimi
A unsetting mental hospital was located far from the citys, it was unknown for residents of any nearby city, but, for authorities, and other mental hospitals in the region, it was well known.
Humans that have comitted heinous crimes wold be sent here, as a way to "help" then with their horrible mental stability, a simple lie to make others think that this was a safe space for those broken degenerates that needed healing, after being sent there, they were never ever seen again.
One day, a smaller mental hospital was breaking down, it didint had the money to keep its, even if smal, amount of patients, they where normal people, not criminals, just people struggling to keep alive, as a last resort, the hospital sended their patients to "Animal hospital", they didint knew about the context of that place.
A simple mistake led broken innocents directly to hell, a bloodbath hell.