Each creature in this world is born inheriting one of the four elements - fire, water, earth, wind. But most creatures aren't aware of their element and in the ages of peace between the different species, the common knowledge about the elemental magic got almost lost and forgotten.
Animals that are able to use their elemental magic are called "element carriers" and are seen and treated as dangerous criminals. The exception are foxes, who always adapt to fire magic.
Element carriers can withstand magic better than regular animals. For example, getting hit by magic fire wouldn't instantly burn and eventually kill a carrier. The magic has greater effect on regulars though, as they can get easily overwhelmed and killed with the magic since they can barely defend themselves against it.
Each element is weaker to one and stronger to another one. Fire beats wind, wind beats earth, earth beats water, water beats fire.
How they find out
Element carriers don't have a mark or anything that signs them as a carrier. Mostly their abilities and element is found out when they are in a very intense situation, be it a traumatic one or something else that causes strong emotions. Unprepared carriers will most likely loose control and become insane at that time. They're then a severe threat to everyone nearby.
The elemental magic includes more than just casting and controlling the specific element. Some element carriers also are skilled enough to form weapons with it. They ae called "caster". To do that they need to use their element and spiritual energy.
Creating and holding/keeping the magic weapon does weaken the carrier greatly. That's why they can't use it for a very long time. So magic weapons barely get used except in some emergency cases.
Some carriers inherit a much stronger and more powerful version of their element. They are called "destructor", as their powers led to great destruction in the past. This is also one of the main reasons element carriers in general are feared by regulars.