Interesting choice in IN Reimu. I feel like this version of Reimu gets me thinking of Hina, as in her ribbons curl a bit, but I think that is just me.
For me, it's Eternity Larva from Hidden Star in Four Seasons. A butterfly fairy was a surprise for me when I first saw this, thinking it would be a bit odd. But then I grew to like it.
The fluttering ring of leaves on her head feels like to me, the ringing of something fresh. Eternity is a fairy of summer, after all. She longs for that heat to catch up to all who seeks and enjoys it. Personally, I see her butterfly wings as an perfect execution of art here. It looks so realistic, and gives the impression that it's very big, and spreads out wider than her span. The hands maybe a synostic reminder to Rumia, but hey.
Her clothes design, for me looks natural. Yes, butterfly gradients follow the top, but then it splits down at the bottom of the dress with leaves and rock patterns (it seems, sorry if it isn't) caressing along the dress, making her feel like she belongs to the nature, and the flutters of life belong it.
All in all, its lovely, and probably stuck with me the most.