Everything on Luxos is made of "light," a compound and force sometimes colloquially referred to as "ki" or "magical energy." Light is not only present in every entity and lifeform, but it also flows in a "pure" state in the atmosphere. People on Luxos have the potential to manipulate this, but it can only be unlocked through the favor of a Beastlord. The type of light a Luxic person would be able to manifest and control after a Beastlord's influence is known as an aspect.
Aspects are defined as the specific type of light a Luxic person (or other sentient lifeform) can manipulate. For example, someone with a water aspect is able to transmute pure light into water and control it. This person could also control water that is already present, such as from rivers and oceans. Aspects are obtained from one of the four Beastlords, and each aspect is specific to a certain Beastlord. Aspects are generally obtained at the moment of creation (i.e. birth), and the reasons one receives an aspect are rather arbitrary.
Aspects are powerful and versatile, and society has explored many applications and techniques over time. However, despite its great potential, there is a limit to one's ability to use an aspect: as one uses it, cael builds up in their bloodstream. A dangerous waste byproduct, high cael buildup can lead to serious consequences (and ultimately death) if left untreated or unaccounted for.
The great majority of people on Luxos are able to use one (and only one) aspect. However, Keepers (those born with special bonds to the Beastlords) are able to use up to three depending on the Beastlord they are linked to.
"And in the absence of light, there is darkness. A gaping hole in the self where life once shone. But even in the empty, lonely darkness, we can draw power. Let me show you." - Lance
When Luxic people use their aspect to manipulate light, a harmful magic compound builds up within their bodies. This is cael, a substance of dubious composition that manifests in the bloodstream. Low cael buildup manifests as exhaustion, fatigue and muscle aches. Though cael within the body will dispel on its own eventually, rest and hydration will speed up the recovery process. Some people dispel cael more quickly than others due to a biological predisposition (such as a higher metabolism).
In higher accumulations, an individual may suffer a condition known as caelism. Common tells for caelism include weakened or impaired bodily functions (such as difficulty breathing or slower wound healing) and a telltale "bruising" or "blighting" across various parts of the body. Caelism takes a great amount of time to run its complete course before recovery. Generally, this amount of time is far more than most Luxic people are comfortable with waiting for, so specific medicine has been developed to break up mass amounts of cael in the body for quicker healing.
Though caelism is very dangerous, prognosis is rarely ever certain death. Caelism initially presents itself in a localized area - if aggravated, it will travel to the user's heart, where it will likely become fatal. Once symptoms are recognized, it is recommended that the user find immediate medical care and rest accordingly. It's considered common sense to avoid using more magic at all costs once caelism manifests.