Thirty years ago a strange phenomenon called a "spacequake" devastated the center of Eurasia, claiming the lives of at least 150 million people. Since then, smaller spacequakes plague the world on an irregular basis. Shido Itsuka, a seemingly ordinary high schooler comes across a mysterious girl at the ground zero of a spacequake and learns she is one of the "Spirits" who are the real cause of the spacequakes that occur when they manifest themselves in the world. He is recruited to make use of his mysterious ability to seal the Spirits' powers thus stopping them from being a threat to mankind. However, there is a catch: to seal a Spirit's power, he must make her fall in love with him and kiss him.

The distant future: Humanity established the mobile fort city, Plantation, upon the ruined wasteland. Within the city were pilot quarters, Mistilteinn, otherwise known as the “Birdcage.” That is where the children live... Their only mission in life was the fight. Their enemies are the mysterious giant organisms known as Kyoryu. The children operate robots known as FRANXX in order to face these still unseen enemies. Among them was a boy who was once called a child prodigy: Code number 016, Hiro. One day, a mysterious girl called Zero Two appears in front of Hiro. “I’ve found you, my Darling.”

100 years ago, the last remnants of humanity were forced to retreat behind the towering walls of a fortified city to escape the massive, man-eating Titans that roamed the land outside their fortress. Only the members of the Scouting Legion dared to stray beyond the safety of the walls – but even those brave warriors seldom returned alive. Those within the city clung to the illusion of a peaceful existence until the day that dream was shattered, and their slim chance at survival was reduced to one horrifying choice: kill – or be devoured!