Touhou In'yashou

The protagonist is lost within the forest located in the mountains. While searching for an exit, he finds an old temple within it.

That is the world which has been sealed off from the real world, Gensokyo.

Appearing in front of the protagonist is the mysterious miko Reimu Hakurei.

The fate that ties the protagonist and Reimu will begin by satiating her within 3 days.

[from Touhou Wiki]