Just IMAGINE Zero Two coming back from a battle and going straight to meet little Hiro.
He wants to become a pilot, so she decides to help him out by lifting him in one of those training mechs.
But then she takes off the fake butt and offers her own instead, her breasts flattened against the glass because of the lack of space.

>Zero Two pressed up against the glass, her ample chest squeezing and rubbing against her suit's material and the front of the chassis
>Shota Hiro's hands inadvertently find their way onto her dinosaur bubblebutt, making him ashamed as she wiggles it back and forth

>He blushes, clearly flustered. "Is - is this okay?"
>She smiles back at him. "Perfect. It's clear you'll be a great pilot when you grow up. Oh, can you squeeze just a little bit harder?"
>She bites her lips as he does so, then contemplates for a moment. "Say, you'll become Zero Tsu's stamen when the time comes, won't you?"

>He clearly likes her, so obviously he nods in response.
>"Ufufu~ Then Zero Tsu will have to thoroughly train you for that day, right?"
>Hiro nods. He's a slight bit uncertain, but of course he trusts Zero Tsu.
>It leads to them repeating this process daily, for an hour or two at a time.

>At some point, they go further.
>Zero Tsu explains some of the process of piloting a Franxx and of course puts her own spin on it.
>"You see, when the pistil links with the Franxx, her consciousness becomes one with the Franxx. That means that when you make Zero Tsu feel good, Strelizia will also feel good, which is the key to winning the battle."
>"O-okay.."
>She smirks back at him, reaching out to grab hold of her plump buttocks and carefully tearing at the suit, exposing herself to him.
>"Give it a try. Make Zero Tsu feel good, daarin."

>"Hnnh.." She moans out as Hiro's fingers slip up between those plush, bubbly cheeks, stimulating that tight, puckered hole, which twitches in response.
>"D--daarin, what a pervert you are. I didn't think you'd like -that- kind of thing."
>She starts panting, pushing her tongue out between her parted lips, her pussy glistening from the teasing digits.
>Startled, Hiro pulls back, causing Zero Tsu to pout. "What's wrong?"
>"I just thought I was hurting you."
>She shakes her head and sinks her fingers into one of those soft cushions, pulling it out of the way so Hiro can get a good look at the hole.
>"Zero Tsu was just feeling so good that it made her moan. Next, you should put that 'horn' of yours in here, daarin.."
>"H-horn?"
>She licks her lips and does the same for his suit, ripping open the fabric where it covered the growing bulge.
>"Of course," she giggles as his cock flops out now that there is nothing left to restrain it. "After all, it's starting to grow so large now.."