Dungeon Amanojaku

Gensoukyou is under attack by the evil rebel Seija.
Seija's plan is to use the demon's secret treasure, the Uchide no Kozuchi, to incite the youkai to effortlessly conquer Gensoukyou.
You are Hakurei Reimu, the priestess of truth and justice, the protector of Gensoukyou.
There is no way you can lose to Seija and the others.
But Gensoukyou has been turned into a vast labyrinth by the power of the mallet.
To make matters worse, your partner Marisa has become separated from you.
Your mission is to meet up with Marisa, gather your friends, and save Gensoukyou.
Easy enough, right?

Résumé

A doujin game by Morisoba based on the Touhou Project series.