sunny boy books

It had been 200 years since the world as we know it was destroyed, and 5 billion people died. Dimensional cracks called gates opened all over the world, and monsters flowed in like an unending tide. No modern weapon worked on those beasts. Humanity was defeated and on the run in just a month. Then, people called hunters emerged, people with immense power. Those people started to push back and created safe locations, which in the future turned into walled cities that guarded the remaining humans.