I own nothing these are other people's characters that I am toying with because . . . . . well . . . . . they didn't get enough episodes.
Set some time before Ariel and before Book leaves.
He thought he was the first to know.
Book was standing in the entry way to the galley when Jayne had once again shot the poor girl down telling her to stop spouting her nonsense. She had been awkwardly trying to be social with the crew that was still gathered after dinner. Jayne was greeted with frowns and scowls as River turned to leave.
Shepherd Book figured he understood the inner workings of Jayne Cobb as well as anyone and certainly better than the rest of the crew on Serenity. He'd taken particular interest in Jayne, watched him and always tried to guide the big merc back to what he thought was his true self. He felt that much of his rough exterior persona; shallow personality and outward lack of intelligence were camouflaged protection. Jayne had played the part so well for so long that even he believed it.
It took him a while to put his finger on it. Something seemed strange about the way Jayne treated River from the beginning and as he learned more about Jayne it finally clicked. Jayne's treatment of River was the same as a young boy teasing a young girl. Sure there was reason enough with River's condition for Jayne to do what he did but that just allowed him to engage her in the only way he knew how. He was blundering along the way any boy might when he didn't even realize he had his first crush. Jayne was a grown man who'd probably never properly courted a woman opting instead for prostitutes. Who knows how young he'd been when he left home. Yes Jayne Cobb was smitten with little River Tam.
Book was quite pleased with himself for figuring it out. Surely the others hadn't noticed it yet. Most of them didn't pay enough attention to Jayne to realize he was capable of anything more than he portrayed outwardly. Mal had a ship to keep running and his feelings for Inara to deal with. Inara had Mal and her clients. Zoe and Wash were too tied up with each other. Kaylee was trying to get the good doctor to notice her. Simon was focused on helping River. River herself was battling to see reality and of course Jayne didn't know why he was pulling pigtails.
River's big brown eyes locked onto his as she passed "boy must see how they broke the bird, become a man, then he can keep the broken bird flying" a crooked grin on her face. He couldn't decide exactly what she meant by it but he was fairly certain he wasn't the first to know after all.