I love how this point out the fact that, unless Reisen have 4 ears, she won't be able to use normal headphones comfortably.

We know Sanae is a more modern day resident of Gensoukyou and as such is often drawn in fanart wearing a current day school uniform. Then we have Reisen and all those old gags about her bunny ears being fake and her looking like a normal school girl without them.

In all the vast multitudes of Touhou doujins over the years has there ever been any that explored a world where Sanae and Reisen knew each other from the outside world before Gensoukyou?

Edit: A possible idea for a story could have Reisen arriving on Earth after fleeing the moon and going into hiding in current day Japan. Enrolling in the same school as Sanae while trying to keep her cover from Lunarian agents sent to take her back or kill her as a deserter. Sanae befriending Reisen while not knowing she is a lunar rabbit but sensing something unusual about her with Reisen then spending some time visiting the Moriya shrine researching about Gensoukyou and Kaguya's whereabouts.

Edit 2: Also with diguised Lunarians sneaking around trying to find Reisen like something out of one of those old alien invaders movies. And Renko and Maribel snooping around trying to investigate Reisen, the Lunarians and the Moriya shrine.