Creation

The creation myth of Astaressa is a beautiful and wondrous story. It is a favorite of many storytellers, who try to give it the mystery and gravitas they feel it deserves. The barebones summary is shared below.

Summary

A goddess sat amongst the stars and learned their songs. She learned their melodies and tunes, and began to create her own. From those melodies came life.
First came the sea and sky, vast and endless. Then came the land, solid and knowable.
The creatures came next: the sea and sky were filled first, and then the land.
Then came the various People: The winged Viceraun, the horned Hukezo. The Elves, made of stars, and Sirens, made of song. The Humans came last of all.
The goddess, pleased and tired, retired to the stars to rest.

Historical Basis

According to the earliest records in historical digs, it seems that the Hukezo and Viceraun did show up on Astaressa long before the Elves and Humans. The Humans are also the 'youngest' race on Astaressa.
The problem with trying to date when the Sirens appeared, however, is that all of their civilization is underwater. Trying to perform archaeologic work below the ocean's surface would be difficult and dangerous. The Sirens also don't seem keen to share any such discoveries, if they've made any at all.

Spread

The barebones are known to everyone on Astaressa. Even if the details vary, the concept of a goddess creating the world and its inhabitants out of music is common throughout all belief systems.

Variations & Mutation

Not only have storytellers added their own flare to the telling, the myth has naturally had its own organic changes and variations as it has been passed from person to person over time. There are other smaller changes. How the various parts of the world were created, what exact combinations of notes were needed to create each race, etc. However, there are two major points in each retelling that shift from person to person. The first point is the name of the creating goddess. The second is what happened after the goddess went to sleep.
The name of the creating goddess may vary from culture to culture. Humans seem to agree it was Theliel, the goddess of stars. The Hukezo and Viceraun believe it was Purah, goddess of harmony and family. The Elves hold the belief that it wasn't just one goddess, but actually a pair - Ashemmi, goddess of song, and her partner Sinaran, goddess of stories. The Sirens, acacording to one account, don't seem to believe in any of these goddesses. Instead they believe that the world already existed and that all the races were travellers in the starry expanse that settled on Astaressa. However this account is not widely acknoweldged by scholars because, as stated, there is only one account of this.
The nature of the creation myth was to simply explain how the world came to be. However, when people started asking why the relations between Sirens and the other land-dwelling races came to be, theologists and scholars started searching for answers. The popular version is that the Sirens became hungry and started trying to feed on the land-dwelling races, and the Humans were the first to push them into the seas and refuse to let them emerge. However, there is a less-popular retelling among the Hukezo, Viceraun, and Elves that the Humans were the sole reason the Sirens never leave the ocean. This version states that the Humans, feeling threatened by the violent sea species, singlehandedly pushed the Sirens into the oceans and told them they were unwelcome on land. In the single account of the creation myth from a Siren, a variant of this version is apparently told among the Sirens as well.