The first time that Bucky Barnes and Steve Rogers had met, just scrappy little kids down an alley in Brooklyn, marks appeared for them both. Bucky got a little colourful shield on his upper left arm, and Steve got a pair of boxing gloves. Neither of them knew how those marks were supposed to represent each other, but they knew that they did. Those marks only appeared when you met your soulmate for the first time, so that's what they were. They were lucky, some people's marks appeared as they passed a stranger in the street and wouldn't be noticed until later, leading to a search for someone else that they'd never actually properly met.

Bucky had been a bit disappointed as they grew older. He loved Steve as his best friend, but society wouldn't exactly allow more and he was a good Christian boy, he wanted to dance with the dames. And if sometimes, when he saw his best friend working on his art, he wanted to dance with Steve... well, that just wasn't allowed. A lot of men and women had soulmates who were the same gender as they were, they were just platonic friends, brothers and sisters. That's how it had to be.

When Bucky fell from the train, the little pair of boxing gloves faded away, the sign of a soulmate dead and gone. When Bucky fell from the train, his arm was severed and, with it, the little colourful shield that should have decorated his shoulder. It didn't matter, the Soldier had no soulmate, the Soldier wasn't human. A weapon had no need for things like that.

Steve met and fought the Soldier, saw his face, and yet no mark appeared. No longer soulmates.

Months after the dunk into the Potomac, Steve would find a little red star adorning the back of his left hand one morning, somehow there overnight...