Rent or Rot: I'm the Landlord of the Apocalypse

The zombies in Nine Dragons Walled City pay rent. It comes in crystal cores, and Ford Clark, who inherited the place after his family put him out in the first weeks of the apocalypse, is the one collecting it. That makes the walled city worth taking, and the relatives who discarded him come back for it. He holds them off with help from tenants who rank SSS. The cores go through the system for supplies. He puts up an automated food plant and starts trading with the base run by people with powers, and he and the base go in together against a crime ring called Pentagram. After that he takes the tenants out to meet the Zombie King.