For the consideration: two soulmate AU concepts for my current ships and beyond.
A. Soulmate AU where you receive a letter from your soulmate once you turn 10/11 and the first letter starts with a single word and then evolves into a paragraph until you come into close contact with them. Then, your paragraph becomes three pages of their inner thoughts and feelings - of triumphs and pain until you both actually met face to face and exchange given names, where a single opalescent scroll pops into existence between you and it details your thought process about your soulmate over the years. And if they die before you met them, the scroll is onyx and have their date of death displayed on it.
B. An AU where you dream your soulmate memories but they’re blurry at first, so you only catch snippets ‘sof clarity. And the closer in proximity you are to your soulmate, the more clear the memories become and they vary in themes. If you accept your soulmate, then your both can speak telepathically with each other and even become lucid dreamers and hop into each others dreams. It if you reject your soulmate, however, then your forced to have a recurring dream of their worst and best memory in random intervals and feel a bittersweet melancholy, even if you didn’t like them or they hurt you.