*edit* The deal on the cover and who's on it is probably that (I think) there were originally two stories in this book.....I think this portion is just one of them. Doujinshi.org actually shows a total of 44 pages, so, yeah....
It is incredibly surreal to see Eirin acting so submissive and, of all people, for Reisen to be the one in control. Hell, I normally start freaking out when people are halfway nice to Reisen, but this? What is happening to my (Touhou) world?!!!