Canon

ZUN is the sole determinant of canon in Touhou.

Only Touhou games, CDs and literature produced with ZUN's involvement are considered to be official canon for the Touhou universe. These are listed under Games, Print Works and Music on the main page.

Uncertain canonicity of PC-98 and Seihou games

Even among ZUN's works, the canonicity of the first five Touhou games produced for the PC-98 platform is uncertain, because in the Windows games, events from the PC-98 series were only vaguely mentioned twice, by Alice in PCB and by Reimu in PoFV, in Yuka's scenario. The only characters from the PC-98 games to appear in the Windows games are Reimu, Marisa, Alice and Yuka, and except for Yuka but especially for Reimu, the Windows versions of their character designs have looked significantly different from the PC-98 versions. No references have been made to any other PC-98 characters since the Windows series started with Embodiment of Scarlet Devil. For example, it is unknown whether Mima and Ruukoto are still living at the Hakurei Shrine, but they have been depicted doing so in a few doujinshi.

The appearances of some Touhou characters in the Seihou games may probably not be canon, since there are no references to them in Touhou works. However, the accompanying story text to Reimu's theme in Shuusou Gyoku, which was included in ZUN's Dolls in Pseudo Paradise CD, mentions a girl that "doesn't look like a human or a youkai" heading to the shrine. This could be referring to VIVIT, who is neither of those and is a robot, heading to the shrine in her game's Extra stage.

Multiple playable routes

When games have multiple playable characters (PCs) advancing through the same levels, the question of which characters did what to resolve the incident becomes ambiguous. Many fans assume that Ending #1 in all games is what actually happened (although there is no proof to this other than the numbering), but if this is the case, then Reimu has won all of her fights except one, against Suika in Immaterial and Missing Power. Some fanworks assume that all of the PCs participated in the incident simultaneously, but fought different enemies at various times, the main priority among fan creators usually being to support the most popular character relationships. In Embodiment of Scarlet Devil, for instance, Reimu x Remilia, Marisa x Patchouli and Marisa x Flandre became the most popular pairings. Many fanmade reconstructions of the game's events therefore depict Reimu and Marisa traveling to the Scarlet Devil Mansion together, and then splitting up so that Marisa fought Patchouli, Reimu fought Remilia, and then Marisa fought Flandre sometime later in the Extra stage.

References in the dialogue and afterwords suggest that indeed all PCs set out to solve each game's incident, although in some games this is explicitly contradicted in the manual where it sometimes says, depending on which character you choose, only one goes out to investigate. Similarly, in Imperishable Night, only one youkai team and one human team are said to investigate.

In the case of Scarlet Weather Rhapsody, most of the PCs' storylines refer to events that happened in other PCs' storylines, making it very likely that all of its playable routes are canonical events occurring at the same time from different characters' points of view.

Non-canon fanworks

Fanworks, most of which consist of doujinshi and fanart, are non-canon. This includes the game Concealed the Conclusion, with its premise about the fundamental nature of Gensokyo, and the Touhou Project Side Story animated video, whose depiction of Lunarian civilization was contradicted by Silent Sinner in Blue a few months after the video's release. The fan comics included in the official fanbook Bohemian Archive in Japanese Red and the semi-official fanbook Seasonal Dream Vision should also be considered non-canon (with the exception of Extra of the Wind, which was written by ZUN), despite appearing together with some of ZUN's work.

Artists who produce both doujin and official work

ZUN collaborates with established Touhou doujinshi artists to illustrate his official print works. However, even if an artist has worked on an official Touhou project, other works by the same artist in which ZUN did not participate are non-canon. For example, Aki Eda is the artist for the official Touhou manga Silent Sinner in Blue, but the storylines she introduces in her self-produced doujinshi, such as the Alice x Patchouli pairing in the "Plastic Heart" series, should not be considered canon. Also note that, despite being considered an official Touhou work, the canonicity of Inaba of the Moon and Inaba of the Earth may be somewhat debatable, both due to its slightly over-the-top comedic gag nature, and due to ZUN reportedly being only loosely involved in its creation. However, due to the fact that some character relationships, like the one between Mokou and Kaguya, can be gleaned from Inaba of the Moon and Inaba of the Earth, it is still a good (if unreliable) source by which to gauge their relationship when compared to other doujin artists like Tohonifun.

Non-canon characters

Some fan-created characters, such as those in the following Danbooru listings, have become memes in Japanese (and in the case of Meimu, Chinese) Touhou fandom. They are popular enough to be drawn by multiple artists, but should definitely not be considered canon.

• Inka Gatensoku
• Mitori Kawashiro (not to be confused with Nitori)
• Meimu
• Sasha Sashiromiya
• Rinbokusan Sasaki
• Karen Yawata

All material relating to yukkuris is also non-canon.

The canonicity of Rin Satsuki is ambiguous: as a character whom ZUN originally intended to include in Embodiment of Scarlet Devil but then deleted before the release of the game, she has never appeared or been referred to in any canon Touhou work. She has occasionally appeared in fanworks.