A place where a great number of youkai moved in long before the time of man, Youkai Mountain.

Usually, Youkai Mountain is just referred to as "the mountain".

The youkai living here have developed their own distinct society, separate from the humans and the youkai living in the foothills, upholding one corner of Gensokyo's power balance.

In particular, the tengu and kappa on the mountain have developed technology (*1) comparable or greater than the outside world's. As such, there exists no youkai who can invade this mountain.

The youkai of the mountain treat one another, more so than any other group in Gensokyo, in the most cheerful and neighborly way. An advanced proficiency in craftsmanship combined with near-futuristic technology means that daily life is bountiful and luxurious.

However, because of that strong internal cohesion, the resistance towards outsiders can be quite formidable.

Trespassers in particular will be chased out no matter the circumstances, unleashing all available power if necessary.

Because of this, the actual state of affairs on the mountain itself is mostly a mystery.

Rumors say that within the mountain exists a large hollow cavity where a futuristic utopia just like the outside world is being built (*2).

In that place, the sun's light shines all day long, an automated factory produces the necessary items to meet the needs of everyday life, and the youkai drink sake while reading the newspaper and discussing the news. One could call it an enjoyable way of life.

Within this hollow cavity, there exists a hole that leads to somewhere in the outside world but opening it is prohibited, so other youkai and humans are not allowed to come near. That's what they say, but...

1: The tengu's technology includes photography, printing and publication. The kappa work with iron and steel and also are skilled in crafting tools.

2: When reading the tengu's newspaper, you get the feeling it's not quite the case.