look the pool #21195 this comic attempts to simulate a touhou game, touhou games include a .txt file called "omake.txt" which includes some extra information about the plot of the game. I assume these pages give a little more information about the plot of the comic.
I love every bit of these. It's a very unorthodox way of making a doujin, and it's especially beautiful that the artist puts in effort in designing danmaku. That, you don't see everyday.