Time Gone By (Miraculous Ladybug Soulmate AU)
Everyone in our world is born with writing on their arm. It has a timer, some reading 18 years, some reading 5 years. No matter the time, it's never wrong. As soon as that turns to Zero, you've met you're soulmate. I've heard of people not wanting that to be their soulmate, so they leave, but the time gets higher as you get further.