@Jeez
In Franxx you have oblivious innocent children which are discovering adulthood on their own, its pleasures, problems, dramas, privileges and responsibilities, but they have to face the authority because it turns out they won't be able to reach adulthood just by pursuing the road prepared for them by the adults expecting them to comply with the present system. They may want their good (\*), but rather than that they are realizing their own goals and using them for their ambitions instead of letting them pursue their own (\*\*).
Sex (\*\*\*) is an important part of it, because sex in japan became abnormal. The same as in the franxx society, where carnality is treated with reluctance. Paradoxically, this lets the kids to explore their sexuality under the radar of their supervisors, unable to recognize the underlying eroticism in their relations.
\*(we still don't know that, for the time being there are hints that they're working against them, but it might turn out "they just wanted what's good for them")
\*\*(it was hinted more than once, that they don't really have to fight those monsters, that it's just for keeping the current lifestyle of the adults)
\*\*\*(countless sexual intercourses are implied through innuendos present during the piloting of the robots, it's japan after all, don't expect them to show teenagers fucking as if it was something normal)
