It's literally about a cute boy meeting a cute dinosaur
they pilot in cute mechs which require a male/female team in order to pilot; almost like Pacific Rim but with a male and a female
They protect their moving cities (plantations) which are primarily inhabited exclusively by adults, who never age nor have children themselves-- the only children are raised in the "Garden" production center, and fight against giant beasts known as "Klaxosaurs" (Screaming Lizards), in mechs known as "FranXX"
Hiro, the MC, looses his ability to pilot and then his piloting partner, only to have a chance meeting with a mysterious girl, who is rumoured to carry klaxosaur blood, has two alluring horns growing out of her head, a set of fangs, and is rumoured to kill every male she pilots with
This is as much as I can tell you without spoiling anything