Spirits and Monsters

Aether is a force of nature, like any other. While it can be very useful - without aether, there would be no magic - it can also be dangerous.
Sometimes, aether forms into beings. Usually, these creatures are not very sentient and are fairly aggressive; they are called monsters. Monsters often cause trouble for travelers, but are not too difficult to fight off. They can take many forms, usually somewhat resembling a regular animal such as a wolf, bear, snake, or bird of prey. Monsters are sometimes found in groups, but usually they do not work together with each other.
Occasionally, though, more sentient beings form. They are referred to as spirits, and sometimes watch over a specific location in nature such as a small forest or lake. Unlike monsters, they generally will not attack humans unprovoked. Offerings are often left for these spirits, and they are sometimes worshiped by humans who live near them. It is rare for someone to try to directly talk to a nature spirit, but it is not impossible. Negotiating with one is considered a great feat.
One of the most infamous monsters, Fenri, fought against and was ultimately defeated by the hero Iliyan, according to Crysian legends. Iliyan himself is said to have been given his wings and magic sword by a benevolent spirit of light. There are no other records of spirits gifting abilities or weapons to humans.
Although spirits and monsters are formed out of aether, they cannot be channeled by a magic user like ambient aether could. Usually they have physical bodies, although other times it is a bit unclear whether a spirit has a physical body or not. Information about spirits is limited by the fact that they are seclusive and mysterious.
While monsters can be killed, the same does not seem to be true for spirits. However, spirits do sometimes fade away after existing for a long time, suggesting that while they cannot be killed, spirits are not fully immortal.