The Night Mother once ruled over the Land of Night. The Land of Night is lifeless, not a single tree grows, and is home to the horrendous denizens of the dark. The Night Mother is the source of all sins and the Land of Night is the embodiment of her evilness. She always watches this land and punishes her people unexpectedly. However, she hates the ray of moonlight that occasionally makes it through the clouds. The Records of Jueyun talk about the Seelie Ancestor and the Traveler from Afar (2nd who came). Who have a story nearly identical to the Pale Princess and the Prince. But how about Kaeya, didn't he come from Khaenri'ah? Yes, but he didn't grow their, as well as his parents probably (unless Kaeya is 500 years old, but in the manga he's shown as a child so it's okay to assume he grows like a normal person). Nonetheless, he still shares the same diamond-shaped pupil the other Khaenri'ahns have. The Prince shone with an extraordinary light. The people of the Moonlight Forest had never seen such vitality. For as the Prince strolled through the forest, life flourished around him: new leaves sprouted and the Princess and her people grew stronger. We now know that fairytales are written in such a way that that the choice for characters makes sense with who they're representing in reality.

It is said that Rex Laps was yet young, the sun was a chariot that raced across the earth. When the three sisters of the night sky were martyred in a calamity, the solar chariot fell into a deep gorge. Princess of the Moonlight Forest, please save my five brothers. We will vow our loyalty to you in return for your kindness," begged a deformed pygmy who had just popped up from behind the branches. So, having sworn to save her people, the Princess and the Prince left the Moonlight Forest and walked hand in hand into the dark forest of the Land of Night. Devastated, the pygmy wandered around in sorrow and regret. He hid the body in a tree hole and walked off alone into the night, and into a self-imposed exile."

The Pale Princess and the Six Pygmies (V)

My theory is based on the identity of the "The Prince", and with information from the 4.2 Archon Quest, I believe that "The Prince" represents the 3rd Descender and tells the story of the creation of the Gnosis.

This wasteland is said to be a land beyond the dominion of the deities, inhabited only by the grotesque ghostly remains of fallen gods, where the former palaces of the Seelie now stand empty.

The Pale Princess and the Six Pygmies (III)

But the master of the heavens, consumed by fear for the rising tide of delusion and breakthroughs, sent down the divine nails to mend the land, laying waste to the mortal realm…” Having slogged across the swamp blazing with dark flames and passed the cave overgrown with poisonous mushrooms, the Prince and the Princess finally arrived at the Kingdom of Pygmies.

Seelie were associated with the moon, having perished along the moon sisters. At the end of book, the people under the rule of the Pale Princess meet the same fate as the Seelie, being forced to live in an undead state. This is currently the most specific description. Which characters are fair-skinned, has light-colored hair, and has bright blue eyes? Khaenri'ahns.It has been thousands of years since the Night Mother captured the Pale Princess, who could be prophecised hero? The traveler, of course.