Ourithanur (our-ih-thane-oor)
The source of all evil, so far as elves are concerned. The source of all must be primordial to those folk; gives 'em a reason not to do anything about it!
The Ourithanur is an elvish term for "great rain," which refers to a cosmic event in which the universe and its creation were blemished by the actions of Melifi, one of the core elvish deities of primordial design. This event saw the cosmic being become the aforementioned "rain" that would fill all of creation with part of the entity's spirit, ensuring all that were created were partially filled with his imperfections. This rain would affect all except the creations under the god Silse, who would give rise to the elves and their homeland. Due to this knowledge, the elves believe themselves to be "spiritually pure," explaining their tendency towards altruism and optimism rather than the deception, greed, and pessimism often found in beings such as humans.
Useful Information
Creation
The elves believe a myth related to the creation of the universe, known as "Creation." This is both a name and event, as it is related to the entity known as Saaurithale; the amorphous being gave rise to the universe by sacrificing its own physical and and spiritual potential. This ancient entity is the source behind all of creation and as such is the origin of anything that has, can, and will happen in the universe.
Part of Saaurithale was dedicated to creating several "children" who could guide the universe on cosmic levels. This resulted in entities such as Melifi, Silse, Aulithe, and Guilime guiding the future of the universe in different ways.
All of the aforementioned beings were able to create different aspects of the universe with their incredible capabilities; however, Melifi was an exception to this rule. Melifi was the lone being created with the purpose of teaching, guiding, and changing rather than creating. Melifi would grow jealous, breaking himself down into the "Great Rain" that would corrupt the rest of the universe.
Corruption
Melifi was a being of incredible knowledge and capability, but he was not as lacking in jealousy as was good for the universe. The part of Melifi present in all of the universe is that of corruption, malevolence, imperfection, and discord. His presence in all things is why death must occur, why animals must kill to survive, why individuals lie and cheat, and any other ill within the world.
The elves believe themselves and their home to be free of this corruption, though it was reintroduced by the creation of the dark elves. During the dark era of Ettermiddag, the elves who had been manipulated and fooled by the Ithitar would have this darkness reintegrated into their spirits. While the devils who caused this conflict expected destruction and chaos, they were baffled to find that the elves continued living in harmony with their cursed cousins, all thanks to their own protection from such corruption.
Control
The belief that all things contain this corruption has given rise to several theories about the properties of the universe. For example, if all things are tainted by the Ourithanur, what would one be capable of if they could control this corruption? Could they control the actions of others? The very ground the world is built upon? Could they manipulate reality itself? This is a question that plenty of individuals have sought to demystify, still with little in the way of answers.
The control of this corruption could lead to any manner of good or bad for the world. For example, could chaos and moral evil be removed from all living things? Perhaps illness could be vanquished and all life could feed upon the sun as plants do. On the other side of the coin, though, could all life be dominated by control of the corruption? Could the entire world be held within the palm of those with nefarious goals? At present, these questions are left up to the "Ourithanur Collective," a group of eastern elvish researchers. While their goals were once malevolent, they have been reinvigorated in recent centuries after their darker side was revealed to the River Kingdom of Nim. With a new outlook and hope of manipulating this corruption for good, the world can rest easy knowing that the Ourithanur could be subverted for the well being of the universe.
All art made by Smokingbat7906 in Midjourney*
It is interesting how this myth would give the elves a huge sense of superiority! I like that you approached it from different angles as well.