Elementals are immortal entities, existing entirely as sentient natural elements. They are composed of a mixture of Aether and one of the Five Elements. Each elemental is composed of a singular element or combination of elements.
Personality
Elementals tend to be reserved and patient. To them time is relatively meaningless as they are immortal. They have passions and excitement like any creature but tend toward expressing such things only when solitary or with their own kind. This doesn't mean it is true for all elementals, only the majority. Overall they find the ways of mortals to be puzzling and view mortals as transit beings whose entire life is as gone in a flash.
Abilities & Skills
Elementals are experts on their particular element and have perfect and complete control of that element. They are also experts on all of the living creatures within their domains, such as an Air Elemental would be an expert on birds and other flying things while an Earth Elemental would be an expert on plans, rodents, and things that live in the ground. This is also per-world, as each world has a different biosphere. Oddly this does not include sentient beings such as humans.
Shapeshifting
All elementals have the innate ability to change their shape and composition. Unlike magical or psionic spells which change the shape of the caster or a target of the caster using a pattern of elements, elementals have the unique ability to form their particular element into any shape they desire, except for another element. As an example, a Fire Elemental cannot become water. Elementals will often use this ability to travel as some form of their element quickly, such as an Earth Elemental turning into a dust cloud or a Fire Elemental turning into smoke.
Transmogrification
Elementals also have the ability to absorb a material into themselves and change it into their chosen element, usually temporarily though they can use this ability to consume something. This allows them to take materials, animals, plants, and other such things with them.
This can be used to transport non-elemental creatures vast distances at incredibly high speeds. Elementals are not hindered when in their chosen element and thus can achieve speeds impossible for anyone else.
Travelling
Elementals can travel to and from any instance of their chosen element nearly instantly.
Society
Elementals are immortal creatures who believe it is their purpose to protect the environment and particularly life within their environment from intrusion. They hold themselves higher than mortal beings and have a long memory, able to trace their existence back to the very beginning of life on a given world or in a given area.
Mortal Interaction
As a group elementals tend to hold themselves above mortal life and thus stay away from most mortals. Overall the group prefers to remain unseen by the mortal world and largely succeeds at this. They will observe mortals from time to time, mostly out of curiosity, but rarely interact with a mortal directly. There are exceptions, of course, a mortal who is particularly helpful as a guardian of life will occasionally be seen as a friend.
Elemental Interaction
Each elemental group tends to stay within its bounds but there is no animosity between them. A Fire Elemental has no animosity toward a Water Elemental even though water and fire often cancel each other out. Elementals will call for assistance from another element if the need arises and there are occasions for them to gather and exchange information, ideas, thoughts, and philosophies with each other.
Gender
There is no true concept of gender within elemental society. There are neither true male nor true female elementals in any kind of biological sense. Rather most elementals would most closely identify to a female archetype. While humans and other mortals tend to see what they cultural perceive as male and female elements as male and female elementals, this is a human construct. The difference is in personality and how an elemental will choose to present itself if it needs to interact on such a level. At the core of their identity elementals believe they are the guardians and even sources of life, they are caregivers and protectors. They do not see males as being either of those things. This is in line with development of many embryos which start off life as female until hormones or genetics direct them to a specific biological sex.
Sexuality & Reproduction
Elementals enjoy what they consider to be intimate interactions, by which they combine their essence (element of choice) with another and share thoughts, feelings, and such for a time. For them this is the closest they get to a sexual encounter. It is a purely cerebral and emotional experience for them. Elementals do not reproduce sexually, though they can create new elementals this is only done in the most extreme of circumstances. Since elementals are immortal a new elemental would only be created if the need arose. When they need to reproduce it is done asexually and one elemental is split into two, each elemental then is a new elemental and some personality traits are only retained by one or the other. Once split each elemental develops along its own unique path though sharing the common ancestor who is effectively gone.
Hybrid elementals are also possible, though far more rare. Just as one elemental can split into two entirely new elementals, two elementals of different types can combine and then split into two hybrids. This allows for things like Ice Elementals (Fire & Water Elementals) and other such hybrids.
Susceptibility to Aether
Since elementals are entirely amorphous and fluid entities in their natural states who exist as personifications of an element of Aether itself, they can be overwhelmed by powerful flows of Aether. This power is another reason why elementals tend to stay away from mortals as it is entirely possible to use powerful magic to overwhelm an elemental and bend it to the will of a sufficiently powerful / skillful magic or psionic person. This does not happen often and they keep this a closely guarded secret. Very few mortals, even powerful and highly trained magic users, know of this or how to accomplish it.
This susceptibility is not a weakness, rather it is the result of the very nature of an elemental. In a direct contest of wills an elemental will nearly always win out over a mortal, leveraging its long life span and wealth of strong memories against the mortal. Since a skilled magic / psionic user knows how to bend the elemental forces to their will, it follows that a sufficiently powerful and skilled practitioner could do the same to an elemental.
Taking Mortal Form
Elementals are capable of fully taking the form of a mortal, this can be anything from a fish to a bird or even a human or other sentient being. When they take such forms they are subject to the same mortal dependancies, quirks, benefits, or issues of that form though they retrain their abilities and memories. When taking on a mortal form entirely they must return to their natural state usually once a day as it takes significant energy to maintain such a form. Most elementals will not take the form of a sentient mortal as the emotions and sensations native to the species can quickly overwhelm an elemental.