(modern setting)Fort Ironwall is a class 5(highest prison class) prison intended for lifetime sentenced prison inmates located just off the shore of the Cold Region.The Guards consist of both mamono and humans with a manticore for a warden,the inmates are also both human and mamono.The prison has Guards with bullet-proof vests,guns(with DE silver bullets) and stun-canes patrolling the AO 24/7,Cameras that  watch over the prison like hawks stalking their prey,Walls made out of solid concrete with a height of some 20m up into the air with barbed wire on-top off them, contraband detectors around pretty mouch all entrances etc.
Basically if you enter this prison ya never leave it,and now a prison buss filled with the latest arrivals enter this hell-hole.
Will they escape?or will they live their days out as sex-toys for the dominatrixes? :P.
IDK Let's find out!.