Lore 2: The Divines, Arceus, and The Chosen.
There are legends of times before Arceus. While it is commonly believed that Arceus constructed the known universe. That's not the case.
At the dawn of existence, there existed 3 Divine entities. These entities were Elysium, The Divine of Light. Eternity, Divine of Darkness. And Evolution, The Divine of Shadow. Those were the ones responsible for the creation of reality. After meticulously using their resources to create every element, every law of physics, they desired more. So they decided to finally create life. This life started on Earth, the most hospitable planet of their creation. These life forms were called the Precursors. Each of these precursors had elements of their own, Time, Space, Matter, Gravity, Void, Fear, Purity, Blight. All of these elements were unique to them, as the Divines did not create them. For years, the Precursors flourished, they flourished so well that the Divines decided to show themselves to their creations. Instead of rejoice, however, The Precursors took sides, They formed cults based on the one of the three Divines that they believed, the cults then destroyed each other. However, there was one Precursor who survived.
This Precursor was one of the few who embraced all of the Divines. His name was Arceus. The Divines had little resources and could not bring back the precursors on their own. After much convincing. The Divines entrusted the rest of their resources to Arceus and fell into slumber.
Arceus, now with the power of all three Divines, and being born with the Matter Element. Arceus rebuilt the world, attempting to create Humanity and Mew, the first Pokemon. However, his creations were unable to survive on their plane of existence, so Arceus devised a plan.
The reason why the precursors were able to live was because they controlled the elements that shaped the fabric of their reality. So Arceus created Dialga, so that they could be affected by the flow of time. Palkia, so that they could live on the same plane of existence, and Giratina, so that they could be affected by the pull of gravity.
However, Giratina was unable to use its power efficiently, and thus was sealed away in it's own pocket dimension to practice it's powers. Finally, after millennia, Giratina was welcomed back into the universe and created stable gravity for the entire universe. Palkia too, made an error in creating space, accidentally creating a planet that occupies hundreds of areas of space at the same time and connecting it to the Continent of Nocturnia on Earth with wormholes that link to any of the planets. As the issue wasn't major, the group decided to leave it be.
Arceus tried again, and it worked. Humans were formed in Africa, and Mew on Celatia. Arceus, remembering what happened to the Precursors, decided to send in a countermeasure to help prevent unnecessary conflict. He synthesised each of the Divine's elements, as well as the Precursor's elements and sent them out into the world. Creating the first Chosen, holding the world's power in their hands in order to help keep balance to the world either by stopping evil or becoming evil.
The most powerful 'Aspects' are the ones granted from the Divines themselves.
Light, the representation of Elysium. Light Chosen are granted the ability to manipulate light into various forms: Balls of energy, blades, floating spikes, as well as being able to travel short distances at light speed, turn invisible, and create illusions. While Light is generally seen as good and heroic, there's nothing stopping a Chosen of Light from being evil, too.
Darkness, the representation of Eternity. Darkness Chosen are the more violent cousins to Light Chosen. As they can do most of the things that Light can do. Again, the same rule applies, Darkness Chosen aren't necessarily evil.
Shadow, the representation of Evolution. Shadow Chosen are a hybrid, a mix of the Darkness and the Light Aspects. However they have unique powers of their own, such as being able to replicate shadowed versions of objects.
While the Divine aspects can either be obtained hereditarily, they can be granted through certain rituals and with the permission of Arceus. The Precursor aspects, on the other hand can be learned through study and practice, with some exceptions.
Time, allowing those gifted with it to control the flow of time to a short extent.
Space, allowing those to warp space to their liking, such as having a pocket dimension inside a backpack or teleportation.
Matter, allowing chosen to create any non-living object they desire.
Gravity, also known as force, lets chosen manipulate the forces on an object, effectively creating telekinesis.
Fear, one of the precursor aspects that are granted through genes and rituals rather than practice. Grants the user control of a target's mind by playing on Fear, generally this is considered an Evil aspect and thus is rare.
Blight is an aspect granted only by exposure to another Blight Chosen or coming in contact with blighted objects. Blight allows the corruption of matter and mind. Organisms that are affected form a sort of hive mind, with the sole purpose of corrupting everything.
Purity is the antithesis to Blight, existing only to repel Blight. Can cure afflicted areas and entities.
Finally, The last aspect is Void. However, of all the Aspects that Arceus was able to recreate, the only one he couldn't synthesis was Void. Little is known about the Void aspect. However it is believed that Void was considered destruction incarnate, and was rare among the precursors.
Many of these Chosen exist today. However to those who don't know the myth, they don't exist at all. As there are about 100,000 Chosen today, that's few enough that it is hardly known. Regardless, those who receive Arceus' gift know their purpose and see it through with full intent.