In the distant future, humanity is forced to reside in massive, mobile fortress cities due to fear of attack by giant monsters called Klaxosaurs. Klaxosaurs can only be fought by Franxx, giant robots that can only be operated by a male and female pilot working in unison. Dr. Franxx and Zero Two arrive in one such city to develop his latest Franxx. Hiro, meanwhile, is left depressed after failing his test to become a Franxx pilot and synchronize with his partner Naomi...