A Game That Saves Humankind

One day, Doppo, a high school boy, suddenly heard a voice from his phone telling him "The game has begun" and that the "chosen challengers" have been taken to another world. If they complete their mission, they can return to their original world. However, this new world is filled with terrifying monsters... Can they survive and return to their original world?! The survival game for humanity's salvation has begun...!