Once again, an incident has befallen Gensokyo. Strange men with bags on their heads have appeared throughout the land, harassing the populace. The native fairies have grown confused and restless, lashing out at anyone they see. Perhaps most troubling, near-exact replicas of the more powerful of Gensokyos citizens have appeared, whose vicious attacks have some intelligence behind them. Two people set out to solve the incident: the Hakurei shrine maiden, as usual, and a certain bored celestial, who figures a fight is a good distraction. The Disappearing of Gensokyo follows the latter, Tenshi Hinanawi, as she gets reluctantly caught up in the incident.
Source: N4G PC The Disappearing of Gensokyo – ChristCenteredGamer