This is just something short that popped into my head and wouln't leave until I booted it out into the world. Enjoy, and leave a comment if you like.
Bucky Barnes is fire. For Steve he is the warm, welcoming hearth-fire that he can always count on to warm his bones and keep him alive on cold winter nights when blankets just won't do. For those who would hurt Steve, he is a roaring inferno that scorches their lungs and leaves them burt and regretting the moment they'd thought they could get away with hurting Steve Rogers.
In the army, Bucky is a candle. Easily underestimated, forgotten, but still capable of setting an entire house ablaze when the enemy least expected it. When he's captured, Zola almost extinguishes the flame, but Steve is his gasoline and he blazes brighter than ever before when his friend, his brother, comes to get him.
When he falls off the train, he is almost snuffed out. The snow surrounds him and his heat isn't enough to melt it away. Hydra sweeps cinders over his embers and begins creating something new.
The Soldier is ice. At first he is little more than powdery snow on top of the sleeping coals, but soon he begins to form into something bigger, something that one little spark cannot melt away. He is the patch of ice on the road that Howard Stark drives over one fateful night. He is the rouge icecicle that falls from the eves and strikes whoever is unfortunate enough to be in its path dead.
He continues as this for countless decades, they pass by with glacial slowness, each one forgotten in its turn like ice falling from cliffs in the cold places of the world, there is only the jagged remains of where memories once were.
Given enough time, and the right fuel, fire can burn through anything. Melt metal and ice alike. Seeing Steve again is like throwing rocket fuel onto the coals and Bucky Barnes returns with a vengence. The Soldier was forced back. lest he be melted into nothing and Bucky dove after Steve, directly into the Potomac. The water can do nothing against him, he is the grease fire that Steve once started in their kitchen and then made the mistake of trying to smother with water.
He is careful not to burn his best friend (his brother) as he lays him on the bank of the Potomac. Then he stays and keeps him warm until the winged man arrives. Bucky surrenders Steve's care to him, hiding in the trees and vanishing like smoke when he's sure his charge is safe.
He will find Steve again, when he's melted the Soldier away into nothing but a harmless puddle of water that can't try to hurt him again. Until then, its not safe. But one day, one day he will return, a pheonix risen from the ashes.