Hidden in the mountains of central Japan, an old, dilapidated Shinto shrine overlooks a forlorn valley. Long since abandoned, only birds and beasts live here, and nothing of value remains for the prospective explorer. If one knew just where to look, however, or had a good dose of luck-- whether good or bad-- one might just find themselves stumbling through a magical barrier to another world. Encompassing the valley and existing just slightly to the left of our own reality, Gensokyo is a fantastical world of gods and demons, ghosts and monsters.

Peaceful, boring days are rare here, as squabbling youkai vie for dominance and meddle in each others' affairs. A strict set of magical dueling laws, known as the 'spell card' rules and codified by the shrine maiden, level the playing field for even the weakest spirits, and keep all formal combat strictly non-lethal.

By and large, the balance of power maintains itself without the shrine maiden's interference-- some bottom-barrel youkai still eat humans, and the humans of Gensokyo's lone village exterminate them in turn-- but on occasion, a powerful youkai's plot is so large and disruptive to the whole of Gensokyo that it obliges her to range out and beat the stuffing out of the perpetrator(s), assuming that one of her friends doesn't get there first.

An Incident.

Unbeknownst to the sleepy Land of Illusions, the 27th of May would be one of those days.