Genetically engendered zombies. Originally meant to be used as a biological weapon in WW2, they were never put into action. The years passed, the war ended but the infection was still kept in a lab, secretly being stored.
The year was 2002 when the breach happened and the infection got out. However, it was only noticed after the four year incubation period but by then it was too late. It was a struggle at first— billions died all around the world but then more died when the nuclear power plants began to meltdown due to the lack of maintenance.
The ever promising internet was dead. Modern technology was useless. Everyone carried around weapons to fight back. People had to figure out how to grow and catch their own food again but with the threat of zombies ever present. Not all technology was dead— there was what had been considered primitive technology from up to the 1980s', but it was now considered a luxury and few had it.
But worst of all, people died from preventable disease. They knew the diseases could be cured! Everyone knew of penicillin, but barely anybody knew how to make it or had the supplies to do so. People knew to clean their hands before eating but they just didn't have anything to clean them with. People knew that disease was transmitted thought bacteria, but they just didn't have the supplies to deal with it. The only hope was ability users— they were in organizations, keeping protection over an area. Only they had some access to slightly above the basics medical care.
Japan's zombie situation was worse— there had been many people, who were now zombies and they were completely isolated from any other land. It was inevitable that the zombies would take over due to how isolated the humans were.
Mori had been the leader of the now collapsed Port Mafia. He had been living in one of the zones protected by someone with an ability, but said ability user had grown weak because of a bacterial infection and died.
The town was overtaken by zombies.
Mori was now alone, travelling without much ammunition, trying to find another community to take him in.
He was going thought an abandoned town, keeping a watchful eye out for any zombies. The only weapon he had left was a knife. He had long ago ran out of ammunition. But he kept the gun itself, hoping to find some ammunition eventually.