Caldera is running on literal fumes when the Insecticon offers him an energon line, disconnected from its own frame on one end, with its thick energon welling up in the tube.
There really isn't much of a choice involved in accepting it. Caldera has lost a lot of his pride over the time he has been scraping by here.
The Insecticon never denies him after that, even after they start finding Cyberfauna to drain again. It's not the kind of fuel that would get wind under Caldera's wings, but there's something about it.
And then, on a whim, Caldera once returns the offer to the Insecticon.
Instead of drinking from the line, the Insecticon attaches it into a fuel port on its frame. Caldera's optics widen, and he scrambles to do the same.
Caldera's frame always tries to filter out the excess metals and everything else dissolved in his Energon. He's been scraping his filters clean and re-using them for who knows how long now. His Energon is thin and flowing and the feeling of the Insecticon's Energon in his lines is different. It's higher in temperature and all Caldera can think of is molten lava but good. His fans kick up a notch and he can't tell whether it's from the heat or the heat suffusing his circuits.
Caldera watches the Insecticon with fever-bright optics. It leans close, nuzzles its fierce face against his cheek.
Caldera can't help himself.
It's been so long since he's last felt this kind of touch. He can barely remember what he'd said, before-- he can only remember the venomous tone and the loathing he'd denounced the Insecticons' mere existence with, but the why just isn't there.
When he kisses the Insecticon's face feverishly, all but crawls into its arms, it doesn't respond. After a moment it places its heavy-arm claws atop his hands, stopping them where they are. It trills questioningly at him, like it thinks he doesn't know what he wants.
Caldera begs it to touch him, please, please.
Afterwards he wonders why he doesn't hate himself for what he has done.
He wants more.
He has a newfound taste for the Insecticon's strange cord, its texture and ridges and the way it locks their frames together, almost forcing a post-coital cuddling session.
But the fuel interface is something Caldera can't get enough of. It's like crossing cables, but never has he experienced the same primal oneness with anyone as when their Energon mixes together far enough that it feels thick in Caldera's lines and thin in the Insecticon's.
On a purely functional note, Caldera finds his filters don't accumulate as much gunk after they started doing this. Small patches of thickened metal build up inside Caldera's plating, when his frame doesn't know where to funnel the excess of metal into, but he wasn't flying anywhere either way.
He feels like he's standing on the precipice of something when he opens his chestplates for the Insecticon. He knows there's no return when it cups his cheek with its sickle-claws and gathers him in its arms before its chest plating parts for him.
There are a few things Caldera is confident about.
The Insecticon is as much a person as he is.
And Caldera wants to be his, frame, spark and mind.