Given Kaguya's similar appearance to Star Sapphire, I've wanted to see Mokou meet the fairy for a long time.
That's something I really appreciate about Touhou's diverse doujin fanbase: there are so many fun interactions to explore that you never get to see in the official works.
eyes, left hand and right ear looks suspicious, could be AI?
probably just assisted. Symmetry is mostly fine enough to not outright call it as one, but there's a lot of little mistakes here and there that likely points to being a touched up one.