My Contractual Partner Turned Out to Be a Zombie

Two hundred years ago, tens of thousands of meteorites crashed into Earth, and countless terrifying monsters burst out of them. They rampaged through cities and slaughtered civilians. To ensure humanity's survival, the five United Nations built underground cities while fighting off the monsters. In the end, all of humanity moved underground to live. One day, those tens of thousands of meteorites suddenly turned into clouds of green smoke and drifted into the atmosphere. During another massive monster tide, humanity was outmatched and on the verge of being swallowed whole, when a man riding a dragon appeared. He was the first Beast Tamer in human history.