Even in the heat of the moment, it doesn't escape Steve's notice that Bucky's a lot stronger and more demanding than most would expect of an omega. It does startle Steve a little, but it's not a bad thing at all. Bucky pushes back on him and Steve can't help groaning at the sensation.

"So eager for my knot." He scratches his nails down Bucky's back before taking a tight grip of his hips with both hands and then he starts to fuck Bucky in earnest, fingers digging into his skin hard enough to bruise. Another time, he thinks, he'll take his time with Bucky, but right now he's got a desperate omega in heat and he needs to take care of him, fill him and claim him like it's Steve's only purpose in life.