In this modern world, the Ainur didn’t have much influence over the populace. The ages had passed, and history was forgotten by the advancing generations of Men. Mairon knew this, and found himself forgetting as well, barely recalling how sweet the screams of pain were, when he was experimenting in Angband…
He remembered the important things though, such as his first encounter with Melkor, the hammering of the anvil - tuk, tuk, tuk - over and over.
Melkor had a better memory than Mairon, as he was a higher being. But his favourite memories (other than the shine of the Silmarils), was the wine-dark nights, when you accompanied him after a long day of meetings and strategies….
You who was here beside Melkor, even after these centuries.
You who, after the Ring was destroyed, you were the one who pieced Mairon back together, hundred years of labour finally rewarded by Mairon’s beautiful, unblemished body. He swore to you then, to be by your side forever and always, to repay the kindness you had shown him.
Melkor’s form took longer to repair, with you scouring the ends of Middle-Earth (now renamed to Earth) for even a fragment of his soul. You found it lingering on the chain called Angainor, and you gathered it in your hands gently.
Mairon was beside you, though, and with two sorcerers working on Melkor’s reincarnation, it happened within a year. Melkor sprung from the floor in all his Silmaril-burned glory, with the scars of Thorondor shining from his face. Melkor, too, told that he was greatly indebted to you, and would follow you until that debt was due.
Centuries upon centuries later, and you hadn’t called upon either Mairon’s oath nor Melkor’s debt. Why? You simply enjoyed their company, as the three of you were the only remaining Ainur (that you knew of) on Earth.
But maybe it wasn’t so bad. Melkor was in the kitchen, cooking something… odd, and most likely inedible, and Mairon was on the couch, doing skincare and watching a trashy reality TV show. You could get used to this.