In Orario, fearless adventurers band together in search of fame and fortune within the underground labyrinth known as the Dungeon. But Bell Cranel, novice adventurer, has bigger plans than riches and glory; he fights monsters in the hope of having a fateful encounter with a girl. When this happens, it doesn't go exactly as he planned. Thus begins the story of an unlikely pair, a boy and a goddess, both trying to prove themselves, both eager to reach their goals.

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.”

Jinta Yadomi and his group of childhood friends have become estranged after a tragic accident split them apart. Now in their high school years, a sudden surprise forces each of them to confront their guilt over what happened that day and come to terms with the ghosts of their past.