GasMaskie
"Wait and Hope"
Aliens. They've got their own planet and their own separate Shinju so it's likely that they're simply aliens that are identical to humans in most regards. I mean, we have total weirdos like Kisame running around who look less human than Kaguya so it's not that far of a stretch.
As for that video, I'm pretty sure the MMD is a program with preset character models and works the same way as SFM does. Anyways White, the infamous Urobutcher ended up writing a Kamen Rider season much like how he ended up writing a magical girl series called Puella Magi Madoka Magica. Can you guess how the plot went?