It's a normal day in Gensokyo when Reimu Hakurei notices a strange fog rolling in. All across Gensokyo, residents witness this fog weakening and killing a great many lesser youkai. At the behest of Yukari Yakumo, she joins forces with Marisa Kirisame, Sanae Kochiya, and Aya Shameimaru to investigate the fog's appearance...

It's a normal day in Gensokyo when Reimu Hakurei notices a strange fog rolling in. All across Gensokyo, residents witness this fog weakening and killing a great many lesser youkai. At the behest of Yukari Yakumo, she joins forces with Marisa Kirisame, Sanae Kochiya, and Aya Shameimaru to investigate the fog's appearance...