A story in the Underground Hell a long time ago.

Kenn's Comment: It's got adorable art, coupled with it being in full colour. Along with having a great story, it's visually pleasing.

While the description is...a bit lackluster, it does more or less sum up the entirety of the story. Think of it as an origins story from DC or Marvel comics. Karaagetarou paints his take on the events leading up to what happens in Subterranean Animalism. Karaagetarou covers the story of why Koishi closed her third eye, how Rin and Utsuho gained their human forms, as well as how Utsuho gained her godly powers of nuclear fusion. Makes for a berry good read, and doesn't necessarily require any in-depth knowledge of Touhou or SA to enjoy, as no gample mechanics are mentioned, and as I wrote previously, what happens in this doujin is essentially a prequel to the events of SA. At times it's funny (largely due to Utsuho), and is often quite touching. A recommended read for those who are interested in Touhou.

Read it at Pixiv, or Danbooru