Sleeves
Puffy sleeves.
Its cuffs are not frilled and has ribbons on it.Wrap skirt secured with clips (!!)Base of the Side Ponytail
At the lineart stage, it looks like it was intended to be drawn clearly differently from other parts of her hairJabot (Necktie)
Looks like it's double-layeredWaistband of the Skirt
There's something like a belt buckle on it
Not present in the final imageSince the back of Remilia's shirt is "custom-made with wing holes covered using bands", there's a high possibility that it's the same with Flandre'sMysterious Circle
Representing a highlight? Or maybe a button?
It was removed in the final drawingThis is a replication of ZUN's rough sketch as seen in the Great Touhou Exhibition.Great Touhou Exhibition Report and Thoughts