They are the very spirits of animals or plants.

Able to convert what they see, hear, touch or taste into thoughts, it can be said that they're like sense converters.

Having no physical body nor specific form, they're similar to air.

They can pass through any obstacle, and they can change their shape at will.

They're often confused with bourei, which are always the embodiments of deceased, but yuurei are not necessarily always the spirits of the deceased.

Some are even born as yuurei, and remain so until they dissipate into nothing.

Also unlike bourei, a single corpse may spawn several yuurei.

Their characteristics are closer to those of fairies; like how fairies are the embodiment of nature, yuurei are the embodiment of spirits.

They can live (*1) anywhere in Gensokyo.

Yuurei that prefer noisy places gather in noisy places, ones that prefer gloomy places gather in gloomy places, and there are even those that prefer hot springs.

They are usually active at night.

It's assumed that because many of them have their existences on the verge of dissipating, it makes it difficult for them to act under sunlight.

Also, their body temperature is very low (*2).

Improper handling may even result in frostbite.

However, this chill can be utilized for one's benefit; for example, during tests of courage.

Passing through a place, as a test of courage, where many yuurei seem likely to gather is a good way to feel a chill on a hot summer night (*3).

1: If it can be said they are "living."

2: Their hearts tend to be cold.

3: Thus yuurei are despised in winter.

The most threatening feature a yuurei possesses is the ability to affect the minds of people around it.

If one is surrounded by cheerful yuurei, they'll eventually feel pleasant.

For gloomy yuurei, vice versa.

For example, the places famous for suicides are often the places inhabited by gloomy yuurei.

Those without enough mental fortuity might even lose their mind, if they happen to face a powerful yuurei.

Also, due to their low temperature, sustained contact may cause frostbite.

Avoiding encounters with yuurei is next to impossible, so all you can do attempt to remain unaffected upon contact.

Generally, yuurei have transient and fragile existences.

Even average humans should be fine if there are only a few of them.

However, it's a different story if that person is mentally weakened (*4).

Keeping confidence in yourself and having no fear is the only way to deal with them.

However, it would be a wise idea not to, out of curiosity, go to places where yuurei gather (*5).

It may result in your mind being shattered.

If that happens, there's no other way but to seek an exorcism from a professional (*6).

On the other hand, there's currently research about the possibility of correcting one's personality by means of deliberate yuurei possession.

This technique is expected to dissuade someone from committing suicide or helping someone overcome their dislike of vegetables.

It's almost ready to be put into practical use, once a method of capturing yuurei is established.

It's not far-fetched to say that the future of human mentality rests on yuurei shoulders.

4: Like when one has just been tricked by fairies.

5: Places such as graveyards. Yuurei often hold live concerts there.

6: But the shrine maiden is not really dependable...