In a world very far away from this one, in a time long ago, there were phoenixes. Intelligent, beautiful, immortal and powerful, they seemed above anything else alive, so much so that some humans worshipped them as divine incarnations of fire, sunlight, and life. A few clans also spoke legends of a great man, an ancient warrior and wise chief, who gained the command and loyalty of one of the mighty avians and so was elevated to a nearly god-like status himself.
At first, the disappearance of the phoenixes was hardly noticed. A phoenix who once frequented a region here or there stopped appearing; people assumed that it had, for some inexplicable reason, abandoned that locale in favor of better ones. Eventually it became noticeable that fewer and fewer were sighted anywhere at all. Many theorized that they had gone home to the Heavens, or to the Sun itself, that it was a portent of the end times and of Life leaving the land.
The last phoenix disappeared. Time went on; the land still prospered and failed in turn, as it always had, and eventually most humans forgot the birds as anything but old, empty legend. Clans merged into great Tribes, then Villages, then Kingdoms, and after a century of alliances, warfare, and conquest, an Empire was born, and the Emperor declared himself a god among men.
But some remembered the Phoenixes and rejected the Emperor as nothing more than a man born in a high position, and so they were hunted, tormented, and killed as heretics and infidels.
One day in the autumn, a group of worshippers were betrayed and caught in their secret place, a location just outside the Rebirth Stones - the last known, or at least suspected, burning place of a phoenix. The Imperial justice favored burning as the death of heretics, since deliberately setting fire to a human body, dead or alive, was considered sacrilegious in the phoenix religions, and it seemed that there was no better site for this execution than the very grounds on which they gathered.
Nothing out of the ordinary should have happened...except for the chance event of one woman burning against the very stone on which the last phoenix died and, long ago, failed to ignite back into life again.
The fire sparked that phoenix's life back into existence, and the power of it also returned the woman to her living form, and by dying and rebirthing in a phoenix's flames she gained the same connection to that bird as that spoken of in the legend from long ago...
^ Little glimpse into what happens when an idea hits me while I draw. Stuff starts to coalesce into theories, plot devices, backstory, etc. This one's still highly nebulous, just a premise really, but there we go.