Punishment can be power.

In a world ravaged by crime and therefore prisons and prisoners a way to escape the system and rehabilitate is only natural. In Metro City, Prisoner 019 has been living his sentence out normally until a strange man who calls himself "Game Master" offers him an unusual reward; a chance to leave the prison for good.

The Game Master offered the "Rehabilitation" to all the prisoners and before long Prisoner 019 is transported into a strange game-like world with strange abilities. However, 019 was not the only person transported here, it was every single prisoner no matter the crime. The Game Master gave one rule:

'Find the Jail Key and be resolved of all your crimes no matter the sentence or the severity.'