The Touhou Project (東方Project), also 東方プロジェクト (Touhou Purojekuto) or Project Shrine Maiden, is a Japanese doujin game series that specialises in shoot 'em ups by sole Team Shanghai Alice member ZUN. Generally, it's a series of 2D (with 3D background) vertically-scrolling danmaku shooting games, that also creates related print works and music CDs. There are also six fighting game spinoffs co-produced with Twilight Frontier, called "danmaku action games." The works of Touhou Project are sometimes called the Touhou Series (東方シリーズ Tōhō shirīzu) for convenience.
The Guinness World Records named the Touhou Project as the "world's most prolific fan-made shooter series.
The setting of the Touhou Project lies in a haunted region of Japan called Gensokyo (幻想郷 Gensōkyō, lit. "Land of Illusions" or "Land of Fantasy"), sealed away from the outside world by the Great Hakurei Barrier. Reimu Hakurei is the protagonist of the project, who lives at the Hakurei Shrine that lies on the said barrier. She, along with the secondary character Marisa Kirisame, set out to solve various incidents that happen throughout the land, mostly caused by youkai. With this, they're both youkai exterminators.
The land is mainly inhabited by humans and youkai alike, who live in their own regions. Humans mostly settle in the Human Village, whilst youkai can be found mostly anywhere, such as the Youkai Mountain, the Forest of Magic and Makai. Some species include magicians, beasts, vampires, ghosts, tengu, mermaids, and kappa. There are other species that could be youkai depending on definition, such as fairies, spirits, phantoms, vengeful spirits, poltergeists, hermits, oni and gods.
Long before the Touhou Project 's story begins, there lived many youkai as well as some humans in the area. After a few humans lost their way into Gensokyo, humans became afraid of approaching this area, although others settled here for the sake of youkai extermination. However, as time went on, humans developed civilisation and multiplied in number, and thus the youkai became distressed about how this would affect the balance between humans and youkai. Thus, 500 years before the events of the Embodiment of Scarlet Devil, Yukari Yakumo developed the "boundary of phantasm and substance", which was favoured by the youkai and protected the balance. This was called the "Youkai Expansion Project" and made Gensokyo a phantasmal world that automatically called out to the weakened youkai of the outside world. Other things that disappear from the outside world, like extinct animals, lost tools and architecture, also became abundant in Gensokyo. Since Gensokyo was a plot of land in Japan that was separated by a barrier, it is Japan that is immediately outside of this barrier.
As a result of the seal, Gensokyo became inaccessible from the outside world, and similarly, those in Gensokyo were unable to leave. Gensokyo's existence could not be confirmed from the outside world, nor could the outside world be confirmed within Gensokyo. As a result, the isolated community developed its own civilisation, different from that of the outside world. Although separated by a barrier, it is a bordering world to its outside, as opposed to being in a parallel universe. There are no seas in Gensokyo, since it is an inland mountain.
In present Gensokyo in all Touhou games, as opposed to the outside world where unscientific phenomena were dismissed as "superstition" by the time of the Meiji era, magical and spiritual qualities prevail. The only known gateway from the outside world into Gensokyo is the Hakurei Shrine. The spell card rules were also established to keep up the relationship between humans and youkai, which is necessary for the preservation of the balance of Gensokyo. The Great Hakurei Barrier, managed by Reimu, was constructed in the year 1885, which is described as a "barrier of common sense" and is thus a strong logical barrier that not even youkai can normally pass through. The youkai were at first against its construction, but then gradually understood its usefulness.
In Gensokyo, incidents occur once in a while, where there's an event that affects all of Gensokyo with an unknown cause at the time it occurs. Touhou games mainly focuses on incidents in its stories, but there are also works such as Mountain of Faith that are about events other than incidents.
Frequently, incidents are due to a youkai's whim or curiosity, and usually Reimu (and on some cases others imitators such as Marisa) would go to investigate it to then find and punish the perpetrator. When a major incident occurs, the spirits and fairies are affected by the circumstances, the incident, and the perpetrator, and experience an increase in power for the duration incident, so there are also cases where a mere fairy can defeat Reimu. It has additionally been stated that people of the village also go out to resolve incidents.
The Touhou Project does use the Gregorian calendar, but since the moon is more important to youkai, there exists the "Youkai Lunisolar Calendar" in Gensokyo, and although it's not used except for some youkai, it features prominently in works that have dates, such as Bohemian Archive in Japanese Red. This calendar doesn't merely take into account the waxing and waning of the moon, but also its colour and the cycles of its edge, and has a 13th intercalary month called Uruu. The smallest unit of this calendar is the month, and the calendar era, called "~th season", goes through a sexagenary cycle. the Embodiment of Scarlet Devil occurred in the 118th season, Immaterial and Missing Power and Perfect Cherry Blossom in the 119th, and Phantasmagoria of Flower View in the 120th. The opening of the "Gensokyo Chronicles" to the public was on the 121st season. This calendar is set such that the end of World War II is on the 60th season.