@Viatos Tentative interest. So we’re controlling flesh mechas? When we upgrade, are we essentially going Dr. Frankenstein on gigantic half-angels? How do pilots control their Nephilim? Telepathically? Is there like a cavity inside the Nephilim’s body or something?
Armored flesh mechas, yes.
You are indeed going Dr. Frankenstein on gigantic half-angels. You may also just be letting them eat and evolve (un)naturally; this is an aesthetic choice, how much conscious control and effort you want your character to expend in this process. Nephilim are capable of "organic" development on their own if allowed, or you can treat them more like traditional mecha and engineer them deliberately.
Pilots control their Nephilim telepathically through sorcery. Most Nephilim have, or can be shaped to have, an internal cavity. Some swallow you. Some have EVA-style entry points. Some you can saddle and ride like giant death-horses. Up to you!