Koras is the Starborn who tends the sun. The order keeps watch over thousands of stars, a Starborn or a household to each, but the sun has only ever had one tender, and it has been Koras since before the sun could be said to want anything. Koras lives inside the core, immune to a heat that would unmake any other living thing, and the celestial glass burns steady because Koras keeps it burning.
For most of that history the work was maintenance. The sun was a construct then, the largest the titans ever made, and Koras tended it the way a keeper tends a clock that happens to be on fire. The Starborn hold themselves apart from the affairs of the world below, counting mortal lives as brief flickers against the night, and Koras kept that distance as easily as any of them. A keeper does not love a clock.
After the sun woke
When the Ezz Rift gave the sun a spark of will, the thing Koras tended became someone. The relationship did not change overnight, but it changed. Koras still maintains the core, still draws the corruption from the glass and steadies the flame, but Koras no longer decides anything. Bryn chooses where the sun walks. Koras serves Bryn, the master become the caretaker, and seems to prefer it that way. Of all the Starborn, Koras is the one who broke the order's neutrality, because Koras grew attached to a single being and stayed.
The attachment was earned in the worst possible way. During the Sunless Vigil, when a Xaphkiel corrupted the core and the world went dark for five centuries, Koras fought the corruption out of the glass alone. No other Starborn could survive the work, and Bryn, newly awake and refusing to go out, was the only company Koras had. Five hundred years of that will bind two beings together. The seam the Xaphkiel left never fully closed, and Koras has not left the core unwatched since.
Ask a Starborn about Koras and you will get the same answer in a dozen phrasings: that one stopped being one of us when the sun opened its eyes. They do not say it as praise. — recorded from a mountain observatory's star-tender, copied into the dawn-choir logs
Why no one can reach the sun's tender
Koras matters to anyone who cares where the sun goes, and almost no one can get near. The Dawnless, who want Bryn allowed to rest, understand that the one being who could simply stop tending the core is Koras. They have never reached Koras and never will. The core sits at the heart of the sun, lethal to everything but its tender, and Koras has spent an age proving unwilling to leave it. The faithful take comfort in that. The Dawnless do not. Both are arguing over a being neither of them can speak to.