Impurity (穢れ kegare), and by extension Purity (清め kiyome), is an important concept in Shinto. In the setting of Touhou it is conflated with the unrelated Buddhist concept of the Pure Lands, and is particularly important to Lunarian culture.
Impurity in Shinto
A central belief Shinto is that certain things can taint a person and their surroundings with harmful impurity. Source of impurity include illness, various bodily processes, contact with death or bodily remains, and various violations of taboo. It is not directly equivalent to the notion of transgressive sin, but like sin, it is a perturbation of the divine order for which restitution must be sought. While there are simple ways to remove everyday levels of impurity, more severe kinds may require a cleansing ritual at a shrine. Various physical symbols of a shrine, such as torii gates and shimenawa ropes, keep the shrine itself pure by acting as spiritual barriers against the impurity of the world profane—and, conversely, protect the world from impurity if the shrine itself is defiled.
Impurity in Touhou
- Impurity appears in Touhou mostly in the context of the Lunarians, who seek to avoid it at all costs and possess a plant which can detect it. Drinking the Hourai Elixir forever taints a person with the concept of death by its absence, and thus Lunarians consider those who have drunk it to be impure.
- Hina Kagiyama collects impurity.
A number of realms in Touhou are identified as "pure lands", which do not possess the innate impurities of the Earth. As a result, time does not exist in the traditional sense; there are no seasons, no day and night, and things do not change or decay (though this is not always obvious to a casual observer, due to their inhabitants creating the appearance of age for aesthetic reasons). Inhabitants of a Pure Land exist as eternal beings, neither alive nor dead - rather than immortal, they are closer to amortal. The Moon appears to be an "artificial" Pure Land, retaining its status only because it has rarely been exposed to impure things; its inhabitants age extremely slowly rather than not at all, and it risks losing its status if too many impurities are introduced. It is unknown if other Pure Lands could become tainted in this fashion.
Kaguya Houraisan's power over eternity allows her to replicate the effects of a Pure Land, either on a single being or over an area; this power was once used to conceal Eientei, and is currently targeted on a bonsai Udonge Tree as a test of her power's limits.
Most of the various Pure Lands are somehow connected to each other.
Known Pure Lands
Since Yuyuko Saigyouji and Youmu Konpaku are inhabitants of the Netherworld, a land even purer than the Moon is, after Yukari Yakumo opened a gap that let them into the Lunar Capital in Silent Sinner in Blue, the Lunarians were completely unable to detect their presence.