It's interesting they chose to give South Korea double eyelids and Japan monolids. I could be wrong but i think Japan actually has a higher occurrence double eyelids than Korea has. Either way a neat detail.
That is Vritra's tail in Riyo's art style, but the shoulder spikes are new.
perhaps these spikes are actually her horns, and Vritra's head is the hooded figure's upper torso (chest & shoulders) note how the hooded figure's speech bubbles always come from the torso and not the (fake) masked head
When you got partners that can defy the laws of physics in their plains it's best to ignore what is possible and instead embrace what has yet to be done.
