Adapted from the manga of the same name by Haruba Onion, the story tells the story of the invasion of the Earth by the monster army 13 years ago. The monsters confronted the Dragon Guardians, a team organization that protects the Earth. Although they launched battles almost every week, the truth is not what it seems. In fact, the monsters were defeated within a year, and the Guardians forced them to play a fake game in front of many citizens who worshipped the Dragon Guardians. Tired of the bullying, the monsters decided to make a change and infiltrate the team to defeat them from the inside.