While enjoying a quiet morning walk, the local shrine maiden Reimu Hakurei stumbles across some curious ruins a short distance from the Hakurei Shrine's gateway. As only one person is allowed into the ruins - and will be well-rewarded for doing so - seven characters engage in a big battle. When the winner enters the ruins, however, they find Chiyuri Kitashirakawa and Yumemi Okazaki, residents of the outside world who have come to Gensokyo in their Probability Space Hypervessel. Their motives turn out to be less than acceptable for the heroine.