Question/suggestion: what would happen if the MC pregged legends while fused? I personally think Ultra Necrozma and the Kyurem fusions would have both halves knocked up since they're integrated into one body. Meanwhile Dusk Mane and Dawn Wings Necrozma would just get Solgaleo and Lunala since Necrozma's off to the side in those.
I could see it going other ways though, especially with Ultra Necrozma since that is Necrozma's canon original form. Interested to hear what you'll say and why.