The mythical world of mountains and seas suddenly comes to real life. Facing the world of mountains and seas, it hangs upside down in the real world, getting closer every day. All kinds of alien beasts, monsters, magical races, and natural treasures fall into the real world. Among them, in order to avoid the destruction of life caused by alien beasts, powerful people have given people in the real world a special ability "criticality", which allows people to temporarily give gifts of alien beasts' abilities, so that they can fight against evil alien beasts and protect their own world.
