This shows takes place in an isolated prison where there are only 4 prisoners and a cat. One day, the prisoners find themselves released because a power outage unlocks all their cells. There are no guards and there is no way to escape. They stumble upon an old man and this old man is the key to everything that’s happening or at least a major part of it.
Norageki is an OVA so there isn’t too much I can say without blowing up the whole thing. I feel it’s well done for what it is and would have been an interesting concept for a movie or at least a short series or something. I don’t know if it would survive a full length season but check it out, it’s only a minor investment of your time.