Natasha and Castle
Castle enjoyed spending time in the lounge, as he was a naturally social creature. The starbase had been awesome and he too was sad to see it go, but he hoped that it meant they were on to new and better things. Contrary to Natasha, he wasn't bored yet. He was on the Starship Enterprise with his wife and a dozen of his favorite sci-fi characters, so as far as he was concerned, he was living the life.
That night he had some vodka and sat at the bar while Kate went around to talk to some friends she knew. Castle noticed Natasha a few seats down from him. He knew who she was, obviously, though he tried to be cool about stuff like that because he imagined it was completely weird to them to have a total stranger know your life story. He watched as she had a glass of wine and then switched to some kind of electric blue drink. He was intrigued.