I Am Reborn in Prison

[Decisive in killing + Machiavellian wit + Not brainless + Growth direction] This is a cage covered with a coat, it exists only for one person... This place is full of demons that eat people without spitting out their bones... Why would an ordinary, ordinary person be brought here? How should he get rid of the shackles on his body and find out the mastermind behind his frame? More importantly, how can he survive with the beasts around him?