The four existing Touhou tags use three different naming conventions:
- touhou-eosd identifies the game through the subtitle, Embodiment of Scarlet Devil.
- touhou-7 uses the game's number, but ignores the subtitle, Perfect Cherry Blossom.
- touhou-7.5 is the same, not using Immaterial and Missing Power in its name.
- touhou-12.8-fairy-wars tries to fit everything, shortening the subtitle of Great Fairy Wars
I'd like to see a standard convention put in place for this series, given that the games are referred to both by number and subtitle.
Some background for those unfamiliar with the naming convention: the games' titles are entirely in Japanese, the subtitles are in English, and each title is ordered by an accompanying number, though the number is not found in the title itself.
As an example, the sixth game in the series is named "Touhou Koumakyou ~ the Embodiment of Scarlet Devil"; the most common way to refer to it is "Embodiment of Scarlet Devil", or simply "EoSD", but "Touhou 6" would be recognized just as easily by most players.
As Justin Time mentioned in the comments, there are a few exceptions to this:
12.3 has the full name of "Touhou Hisoutensoku ~ Choudokyuu Ginyoru no Nazo wo Oe", and English fans usually call it either "Unthinkable Natural Law", from the English translation of its Japanese subtitle, or "Hisoutensoku".
12.8 is "Yousei Daisensou ~ Touhou Sangetsusei", and English fans usually call it "Great Fairy Wars", "Fairy Wars", or (with tongue firmly in cheek) "Faily Wars".
12.5 is "Double Spoiler ~ Touhou Bunkachou", with an English title and Japanese subtitle.