For context; the request talked about The Collector and Reader being friends in a past life, and Reader's reincarnation meeting him again in current time TOH.
Long ago, when the demon realm was empty. Back in the beginning. It was just the stars. Divine beings who pranced freely through the skies. Without burdens, without disturbances— they lived peacefully.
It seemed like it was just The Collector and (Y/N) then; roaming across astral plains, playing unending games of tag and searching for treasure in the starlight desert, diving into pools of stardust to see who could hold their breath the longest. The stars looked upon their friendship with warm eyes and smiles, knowing that the two would grow even closer, and their bond even stronger as time would progress.
Whenever The Collector was spotted alone (which was incredibly rare), the first and most common question that the stars would ask them was, "Where's (Y/N)?" And similarly, whenever (Y/N) was spotted alone, the stars always knew that The Collector was somewhere nearby. The pair was inseparable.
An oath was contracted between the two; and although it was formed by childish resolution, it was a profound and ardent promise— a link that would transcend time and space.
"I pinky swear that we'll be best friends forever! Even if the elders tell us we can't, even if we're mad at each other, even if we're far apart... no matter what happens, we will always find our way back to one another."
Then one day, the gathering rocks and dust that drew itself from the galaxy began to build upon itself, and a planet filled with naught but a boiling sea was born. The blessings of the universe gave rise to life on that planet— the Titans, a species of towering beasts who roamed the oceans of blistering heat. The Collector found interest in these creatures.
He wanted to see one in person, but the elders warned him that too much investment in curiosity was something to be wary of. (Y/N) took their words to heart and remained in the sky, but The Collector chose to be ignorant. Their visits to the new world became more and more frequent. Each time they returned, they would tell (Y/N) of the things they've seen, the creatures they've met— they also mentioned their new 'friends', a group of silly witches that would always answer to his beck and call ("They call me 'The Grand Hunstman' or something."), and a Titan who waded through the seas; carrying an egg wherever he went.
"He said his son was in there." The Collector frowned, "I asked if I could play with him but he said no."
One day, The Collector did not return.
(Y/N) could no longer sense them. It was as if he had just disappeared, like he never existed in the first place.
The worst was assumed, and the heartache of losing their closest companion was too much. (Y/N) fell into an eternal slumber. Time ate away at their fragility, and soon, they disappeared too.
The stars mourned the tragedy, and they continue to grieve. Even now— every once in a blue moon, during a meteor shower— you may hear the cries of a wailing star.
But a promise is a promise, no matter how small. And as sworn, "...we will always find our way back to one another."
And now, the world is ending.
Every witch in the Boiling Isles is trapped— on the brink of death. You and your friends are about to be impaled by the beastly appendage of the Emperor, but as you shut your eyes to brace yourself for the oncoming pain, something stops the attack.
The person in front of you is jarringly familiar.
Once Belos is gone— reduced to nothing more than a splatter of substance— the starry figure turns to you. You get a clearer look of their face and there's no denying it— you know them. You've never seen them once in your life, but you know them. Your eyes burn, and for some reason, you suddenly feel like crying. You feel relieved, happy? Why is that?
"(Y/N)! I've missed you so much— aww, no don't cry!" You didn't even realize that there were tears were slipping down your cheeks.
The Collector rushes to embrace you, but you're frozen in your spot. Something in the depths of your mind is pounding— trying to make you remember— begging you to hug them back. Just who is this person?
"How—" You sniffle, "How do you know my name?"
A laugh, "What are you talking about, silly? Ooh! Are we playing pretend?"
"Huh?" You don't understand. A small silence follows.
Something seems to click in their mind, and suddenly they place their hands on your shoulders and push you back by an arms-length, holding you in place to get a clear look at you. He scans your face; gaze stopping to stare you directly in the eye. It was like he was peering into your soul. Eyes are windows to the soul, and if this saying holds true, then whatever The Collector had seen did not please them. His countenance twists into one of confusion and slight agitation when he can't find what he's searching for.
"What happened to your memories..? Why are they gone? It's like... you're a completely different person." A moment passes as they mentally try to decipher the issue at hand. Luz and the rest watch the scene warily, equally confused as you were.
Distantly, from somewhere beyond the sky, you think you hear crying.
The Collector's frown deepens, realization dawning upon them. They reluctantly let go of your shoulders.
"It's okay..! All that matters now.. is that we're together again!" They smile, "And look! We found our way back to one another! Just like we pinky promised."
The Collector takes your hand.
"You don't have to worry, (Y/N)! I can help you get your memories back! And this time, I'll make sure that nothing keeps us apart."
The distant crying stops.
