The next book of the series! Ghost in the System (Book 7):
The System took over the whole world in an instant, and people lost any ability to communicate with each other. But the deadies weren’t the only ones who could get better. Over time all the peoples of the earth found ways to contact each other, with the System allowing them to trade, communicate, and come to each other’s aid.
What’s more, the existence of a flying city and the ability to teleport allowed them to even personally visit other continents and travel over the sea. But the most important thing was that now they could help not just themselves and their own people, but even eradicate the zombie infection around the globe!
But the question remains, does any of that matter to our hero? He never had much empathy for anybody he met before. But if it came down to saving his home world, then maybe it might be worth changing his outlook?