We have reached a point where Touhou became so popular that we have a doujin story of Touhou about Reimu meeting a doujin version of herself because people were writing doujin about her inside the doujin, just like how we in real life write Touhou doujin. And the doujin doujin became reality thanks to Gensokyo (lack of) common sense.
P.S.: Can't wait to see the reaction of the children when they get to the part where the big bad Mima becomes protag of the week and bullies: A gatekeeper, a girl who has nothing to do with the rest, Alice the Witch of Death, an Ice-manipulating girl and her best friend, a blade-wielding maid, and a powerful bat-winged being.