Apocalypse no Toride

Apocalypse no Toride (アポカリプスの砦, Apocalypse no Toride) is manga written by KURAISHI Yuu and illustrated by Kazu Inabe. It was serialized in Shounen Rival from September 3, 2011 to August 4, 2015.

Plot
What can you do when you're mistakenly accused for murder? Nothing. You just go to prison. Lucky you; your inmates are some of the biggest cutthroats in the prison. Seriously, you are lucky. Especially when zombies attack.