Long ago in the First Movement of the Grand Song, Lyrianur created the Yllren, People of the Stars, to guard and watch over humanity in the dark days he knew were about to fall upon Velair.

And so in preparation for that, he gave them the ability to Fold, to move between the worlds that make up Velair with ease, transmuting into pure energy to pass through the layers of Silence between the worlds. Then when they reach their destination, they resume their physical shape.

Then to blend into whichever world they are in, they can also change their physical appearance to match, transmuting into energy first in instances which require large adjustments in mass.

They don't have a default physical appearance. Rather, full Yllren's natural shapes are pure energy, humanoid in shape and appearance, of variable size and colors. Colors do tend to run through the spectrum of blues, purples, and other cool colors. Eyes are nearly always a very pale glacial ice blue.

Yllren are also capable of some telepathy. Nothing huge or very powerful, but enough to communicate with each other through the Silence and in space, since that is meant to be their primary home. They can also communicate with those whose languages they don't share through sharing the concepts and ideas rather than the actual words.

Food wise, full Yllren absorb radiation and energy from their surroundings and it gets converted to their form of energy. Physical, non-Yllren bodies will require the nourishment that species actually eats and in the same amount.

Probably will add more later. Kind of scatter-brained presently.

They're star people? So the people in your world are stars?

Do any other cultures worship them? Are they messengers? Are they peaceful? Do they ever engage in war? Do they marry? Do they die, or get absorbed by a bigger one of their kind?

Some stars are people and others giant balls of nuclear fusion. It depends on where one is at in Velaiar. Not all people are stars, either. Most are, in fact, completely and totally human.

Some cultures do indeed, and incorrectly, worship them, or what they remember about them from their old tales and legends from the First and Second Movements. Most of the Yllren are very disturbed by it and try to stop it whenever they run across it. It's pretty rare since they don't often interact with humanity anymore.

Are they messengers? Sometimes. Peaceful, depends on the individuals. They were created to be guardians, so they're not conflict-averse, rather their natural view of conflict and struggle is with the goal of protecting humanity. Also yes, they do engage in war.

There was actually a civil war among the Yllren, with many departing from their duty to rule over humanity and other species, while the loyalists tried to stop them. That war lasts a very, very long time and almost drives the entire species to extinction.

Marriage does happen, both among themselves and in their shifted forms with individuals of other races. My MC for the project I'm working is half-Yllren and half-human, coming from one of those marriages. They can die, when a significant enough force is applied to their energy forms to overpower and dispel it faster than they can convert the energy to their own kind. In the course of the long civil war, it was found that the easiest way to kill many of them at once was to cause a star to go supernova and catch them in the blast.

Why was there a civil war? For whom do they sometimes serve as messengers? Why don't they talk to humans anymore?

Oh, because some people decided they could best guard and protect humanity by installing themselves as kings and gods and forcibly ruling them for their own protection. The loyalists rightly believed that to be blasphemous treason and so refused to join and the war broke out after they realized they were only ones who could prevent the traitorous Yllren from succeeding.

Messages are carried for Lyrianur, Utontol, and the Companions for the most part, when taken to humans or other species. Otherwise, yes, they carry messages for themselves of all sorts of kinds. Some are written. Others are telepathic memory impressions that must be shared in detail and scope far beyond what physical means allow.

There just aren't many Yllren left anymore and it's dangerous for them to be seen by humans since that gives their enemy a trail to hunt them down with. They tend to have, except for soldiers and spies, gone to hide themselves in distant corners of the multiverse to survive. The rebels are winning the war in the current time-frame, so they're a bit bolder and will reveal themselves to manipulate and sway people to their cause. The loyalists can't take that much of a risk anymore, since there are so few left.