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If Riku's canonically a Dream Eater, then it stands to reason he'd look like one in Monstropolis yeah?? (monster-Sora already looks like a Chirithy, notice)
Anyways some design notes
He's the same (or adjacent) species as Dean Hardscrabble from Monsters University-- though not a centipede taur for Reasons
(SquareEnix probably prefers consistent proportions across world specific models to make rigging easier, and therefore would not design him Like That)
His wings and elytra are at his waist since from my observation, they like to put things at waist length in Riku's designs. When folded flat against the thigh it looks like pockets.
He would use the lower wings mainly for gliding, to generate extra lift (given the length of his tail)
I'm debating moving the position of the Spirit sigil to his back, between his wings-- 1) that is consistent with its placement in DDD, plus 2) his wings would also contextualize it like a Nightmare
Your honor he's just a little guy
Sora's monstropolis model is a bit uncanny proportionally speaking, but he's still cute if you squint past the weird textures and boggly eyes