Are you sure this is reflecting Classic Reimu and not her predecesor? It'd make more sense if that was simply Sendai Hakurei no Miko...

Artist comment:
紫と霊夢の弾幕漫画後編になります。右上はネタの都合ででてきた初代博麗の巫女さん（デザインは旧作霊夢さん）

Well, it does say that the upper right is Hakurei no Miko, but also adds that the design is classic Reimu.