Following the Interstellar Alliance's establishment of peace across most planets in the universe, they founded the Cosmo Academy. The academy is celebrated as the most elite institution in existence, with its graduates assured virtually any career they wish to pursue. However, admission is restricted to those who pass the entrance examinations conducted every three years, resulting in extremely fierce competition for a spot. Lane Tadatos is a Terran who has advanced to the final stage of the examinations. Assigned to a group of ten, he is dispatched to the Esperanza—a ship stranded in orbit. Their final trial requires surviving 53 days on the vessel, with no means of external communication aside from an emergency forfeit button. Yet, a critical issue arises for the examinees during a headcount: there are eleven people aboard the Esperanza, indicating that one among them is an impostor.