PartyZone

Aye, It is indeed Darling In The FranXX

Here's a little information about it.

In the distant future, humanity has been driven to near-extinction by giant beasts known as Klaxosaurs, forcing the surviving humans to take refuge in massive fortress cities called Plantations. Children raised here are trained to pilot giant mechas known as FranXX—the only weapons known to be effective against the Klaxosaurs—in boy-girl pairs.

Bred for the sole purpose of piloting these machines, these children know nothing of the outside world and are only able to prove their existence by defending their race.

Had to do multiple comments due to the Character limit.