Brock Rumlow doesn't actually like the Winter Soldier, but he is less cruel to him than the rest of HYDRA. In one fic, he tells W.S. that he is allowed to sit after a mission is complete instead of standing for hours. In another, he gives W.S. medical care instead of just counting on the serum. Another time, he gives W.S. food when they're trapped in a cave-in.
The one I remember best the mission start has been delayed, and W.S. is getting restless with spare energy. Rumlow gives him a Rubik's cube to solve, than plays battleship with him. Pierce compliments Rumlow on finding a way to keep W.S. calm enough that they won't need another wipe (which would take extra time), and mentions that procedural memory is retained, so W.S. now knows battleship.
If anyone has a link or knows if the author has reposted it, that would be great! Even if you just recall the fic and know who the author was, I liked their writing style and want to read more by them!