This is a world that humans cannot explore, and the residents here are monsters in the eyes of humans. In a war seventeen years ago, the Demon Ancestor, who had to flee to Earth in order to protect his planet and people, met the newly born heroine, so he sealed himself in the heroine's body to avoid the enemy's pursuit. Seventeen years later, the seal was lifted and the Demon Ancestor needed to return to his throne. What happened to the heroine was an invitation seventeen years ago? Or will it be a disaster seventeen years later? Friends in danger, unknown things behind the lives of loved ones. . . Are you giving up everything for your own happiness? Still. . .