Matt and Serenity arrived at the Merfolk palace much later than they'd thought they would. The Aquarians told time similarly to how humans did, they just had an extra hour in their day. Considering how much larger the planet was to Earth, Serenity was surprised that it's rotation and daylight lengths were so close.
It was a silly thought to focus on, but Serenity's nerves were beginning to get the better of her.. 'Why am I so nervous?! It's just Matt! My Matt.. I can actually say that again without feeling like a clingy idiot..'
When they were children, he was 'Her Matt'. The title made sure that all of the other kids(especially girls), understood that she was prioritized when it came to his time. In turn, he called her Ren. Or if he was feeling particularly cheeky that day: 'His Songbird'.