Copypasted from the Touhou Wiki:
The Touhou Project is a series of 2D (with 3D background) vertically-scrolling danmaku shooting games made by Team Shanghai Alice, with two fighting game spinoffs co-produced with Tasogare Frontier. They are similar to regular shooting games, but focus more on weaving through complex patterns containing anywhere from dozens to hundreds of bullets. Every game in the Touhou series is set in the fantasy land of Gensokyo, and the series is known for its huge cast of characters, well-developed storylines, and related materials such as music CDs and fan-made comics.

Touhou Mahoudan
It seems like some people might be a little confused with Mahoudan. I think I'd better make some things clearer... Some who read this probably already know this, but NOTICE!! As stated in the comic summary...It is AU. NOTICE!! It does not take place after Subterranean Animism. Or during. Or before. There's obviously no such thing as Mahoudan in the actual games. =/
AU: (Wiki copypaste) An alternative universe fan fiction (also known as alternate universe or alternate reality), commonly abbreviated as AU, is a type or form of fan fiction in which canonical facts of setting or characterization in the universe being explored or written about are deliberately changed.
Yep. In Mahoudan, quite a bit of Gensokyo's history and character's background story are changed. Mainly there being the Mahoudan and Kaikidan. Mokou's past remains more or less the same, except she's a member of the Mahoudan in this comic. The Nuclear Fusion power given to Utsuho isn't much of a conspiracy anymore. There might be a number of pairings that would be considered crack pairings outside of Touhou Mahoudan. Also, PC-98 characters are there with the windows characters (which isn't really a point but...)

The author. Is still in school. Likes to draw but draws for fun and has trouble drawing seriously. Is very lazy as well, so it affects the comic badly I guess. But I really like to draw, and I really like Touhou too, so thus this comic was drawn. Favourite Touhou character is Utsuho(quite obviously). Plays Easy Mode. Cleared easy mode for Touhou LLS, MS, EoSD, PCB, IN, PoFV, MoF, SA. Cleared normal mode for IN.