In the world this anime takes place in, there is a story about a bird that has only one wing, which needs a partner to hold close so they can fly.
It's a story about a life that burns brightest when that life is shared with someone special.

And it is a humongous mecha series.

This is an anime that takes you on a journey to a place that feels otherworldly. Even the characters we follow are not quite sure what the rules of the world are, which left me wanting to see more of this universe.
Whilst the anime is about humanity trying everything in their power to survive Klaxosaur onslaught and the ever expanding desert, it's really about this group of 'paracites'. Kids who are sent to pilot the Franxx and defend the moving cities.
These paracites are born and raised to do this

Here is a small spoiler-hook that won't spoil your enjoyment, but might hook you into watching this anime:
At some point in the show you, as a viewer, will probably feel as though

Other shows this anime reminded me of:

• Evangelion. People controlling giant robots to fight giant enemies.
• Pacific Rim. You need two people to control a mecha as the strain will be too much for one person.
• Tengen Toppa Gurren Lagann. The greater then life action scenes.
• Future Diary. 02 will do anything for her darling.

Here a quick list of the tropes and themes that I enjoyed in this show:

• Dystopian future
• Science Fiction
• Procreation metaphors. Tons of them! Mega-city docking procedure is called 'kissing', The Franxx need a 'stamen' and 'pistil' to function...
• Immortality at a price. The "adults" live forever, but in exchange life has become stagnant and dull.
• Forbidden knowledge. The protagonists are kept in the dark about most things and if they obtain some it's considered dangerous.
• Mysterious enemy. For a very long time, no-one really knows what the Klaxosaurs are.
• You are Number 6. The kids are raised to do battle for the Adults, and so are not given names but numbers, they are just Parasites after all.
• We will rebuild. Huge part of the story is humanity trying to rebuild civilization after the world has turned into a great desert.
• Purpose of Life. The anime starts with the main protagonist being unable to ride the Franxx and thus to die in battle, leaving him with existential angst. Enter 02.

The show isn't perfect, I can't help but feel there some lost potential. I wanted to know more of this world then I got. The story seems have bitten more then it can chew when looked at as a whole.
But in the end, it was an anime I thoroughly enjoyed and would highly recommend it.