This Reimu's design comes from zun000.JPG , this image was posted in the old ZUN blog and you can see it here if you are interested
https://en.touhouwiki.net/wiki/Miscellaneous_illustrations_by_ZUN
you can recognize her because reimu is wearing a pink hair bow without frills and because she has a "double" ponytail at the back, they almost look like hair rings, but they are not.
and well, obviously because she wears that red "kimono vest", similar to the one she wore in touhou 1.
in the image Zun001.JPG his design is almost identical, with the difference that his hair bow does have frills
