Touhou Kourindou: Curiosities of Lotus Asia(2003)

Touhou Kourindou: Curiosities of Lotus Asia is a series of side stories that complement the normal Touhou timeline.

Written by ZUN and illustrated by Genji Asai, each story takes up four pages; one full-page artwork, three of mostly text. When serialized in the Colorful PUREGIRL, each story required two months to complete (on average). The stories themselves are serialized in various magazines, now serialized in Dengeki Moeoh.

It's written from the point of view of Rinnosuke Morichika, proprietor of Kourindou, a little odds-and-ends store. Naturally, he has a lot of well-known "customers" in the store, especially Reimu Hakurei and Marisa Kirisame.

(Source: Touhou Wiki)

Note: In 2015 this series was restarted in the pages of Strange Creators of Outer World, an official Touhou Project magazine published by Kadokawa under its Dengeki Moeoh imprint with the full supervision and support of ZUN. These stories have yet to be compiled in hardcover format.