Game of the Universe: Zenith

Arthur Shaw never expected much from life. Between university, his grandfather’s struggling restaurant, and the old man’s worsening health, he had enough problems already. However, even he did not expect Earth to fall in a single morning. Conquered by an alien war tribe, humanity was forced into Zenith, an intergalactic game where every human must pay a monthly tribute, or die. So Arthur finds himself facing monsters, desperate humans, and a brutal system that strips him of any choice from the start. — Description from novelcodex.org