Brock was never afraid of alphas. He doesn't remember that they made him feel anything more than slight apprehension, at school, in training camp or in service. His parents were a model loving couple, his father never hurt mother nor two omega-kids. Nonna could be scary, but it was always aimed at those who tried to argue with the old alpha. And those has always been swept away by the inflexible will of a woman who raised several generations of unruly omegas. Brock did not have any sad or even unpleasant experience, he himself could throw a good punch, and any beta in area would immediately stop a presumptuous alpha, though even alphas themselves - well, who in his right mind will decide to offend omega risking running into a court case? Brock’s Jack is embodiment of love and care. Brock never in his life met anyone as affectionate and tender as his Jack. Even the Winter Soldier - stuffed with a lot of drugs and generally more a robot than a man - even he does not scare Brock.
That is, Brock is trying to say that there has never been a traumatic experience with alphas in his life. He's been injured, been in fights, he has been humiliated by his superiors, but not for the fact that he was an omega and they were the alphas. He's used to them, they're simple people like him. He understands what lies behind their actions, what to expect from them, how to use his nature against them. You can be an unshaven jock, but you can wave your eyelashes, tilt your head to open your neck a bit hinting at the ephemeral possibility with this posture, this gaze, this smell, and then Pierce will smile fatherly to you and sign papers to improve the supply of the squad, Westfahl will give his favorite knife silently, and a terrorist with a grenade in his hands will give this grenade to Brock, kneeling. (Though, if only said terrorist is not an omega - these had to be shot by snipers. Brock has had to aim those from the roof.)
But here is the Captain America who appeared from oblivion... Sunny boy of all nation... Brock doesn't know what's wrong with him. It's hardly a matter of generations. Neither Nonna nor more decrepit relatives didn't make his knees shake at the mere sight of them. Cap's scent is quite natural, without chemical notes like Winter's because of the second-handed serum; slightly salty, probably because of all that time spent in the ocean; but in general it’s like everyone else's: a little gunpowder, a little wood, a little blood. Like any soldier has.
However, Brock doesn’t shiver when deals with any soldiers. With any alphas. Brock finds out about Captain from Pierce at the meeting with Hydra part of the unit, then from Fury, who decided to place restless Rogers to STRIKE. The first moment they were introduced to each other Captain took Brock's hand to touch his wrist with an old-fashioned gesture, familiar from Winter's manners, and his blank expression was instantly replaced with confusion and then with deepest interest. Brock felt nervous and stepped back, physically feeling alpha’s attention swept over his body. Jack instantly materialised behind him without any sound, and his mere presence forced to retreat both Rogers and sense of fear caused by him. Not forever.
Brock feels the look of Captain America’s icy eyes on every mission. Every time he inhales flaring his nostrils as if trying to pick something in the omega’s smell. Brock watches him with confusion, not knowing what is happening. Not knowing why he, who never felt alphas’ brutality, though saw plenty of it on the missions, has his knees shaking and breath hitching with a hint that this particular alpha will step to him, tug him in and bury his face in Brock’s nape trying to bite where Brock already has the mark, gifted him by Jack many years ago when Brock was green rookie barely left training camp and only transferred on active duty.
Brock is afraid of the fear itself. He’s afraid of its inexplicability. He starts watchin the rest of the alphas closely in fear they will cause him the same reaction, but those do not pay attention to him as before and thus do not cause nervous tremor in his hands. Brock digs in Internet, diligently cleaning up search history, so as not to make Jack worry. He looks with horror at some omegas forum where the fear of alphas is described as the clearest sign of pregnancy, and then in the same horror he looks at four pregnancy tests, waiting in bathroom in some diner for them to work. All four of them are negative. Cursing, Brock throws them away, flushes his face with cold water and goes to the Hydra base.
In fact, it is actually the Shield’s base, but there are four underground floors under the main building, where half of the quarters secretly occupied by Hydra. Although on the top floors there are some Hydra’s high ups, so base could be assumed as Hydra’s. Again, it is here Winter Soldier is almost always kept. On the other hand, Hydra kinda does not exist, so the base is Shield’s. To hell with this.
Brock changes, stops by Jack's office, finds no one there, pulls out a chocolate bar from the bottom drawer of the table and goes to the gym, chewing on the move, where he finds the whole squad. When there are no missions their routine is very simple and boring: they train, scoff, discuss and try new weapons, eat, scoff again while digesting food, and then train again. Today Winter Soldier is sent to train with them, cause he’s bored to sit alone waiting for the next mission. Brock is allowed to show several techniques of tai bo to him, they train together for a while until Brock is soaked with sweat. He goes to shower and Winter continues to work out new knowledge with those who are less fortunate.
Brock with Jack and a few guys go into the cafeteria and get in line, and then with their trays move to a free table past the damn Captain America, who first takes a deep breath, then slowly raises his head and pins Brock with his gaze. Although... It seems this time all of them are rewarded with the highest attention. Brock shrugs and follows Jack. Rogers watches them for a while with explicit struggle on his face, but then returns to his food.
...Perhaps Brock should not have to succumb to curiosity, but he has exhausted all possible versions regarding himself and began to dig up information about Rogers. Although ’dig’ is may be too strong a word. He just had to open the first link to biography of Captain America. Of course he read his file. But he read it about his current state, without delving into the past nor looking at black and white photos. He's itching to go cut Winter's hair to confirm or refute his guess, but he’s already realised that the serum-enhanced nose of a super soldier reacts to the smell of Winter clinging to Brock even after the shower.
Brock doesn't know what to do. He can't sneak into the lab and ask techs to wipe his memory. They say none of the normal people could survive it. This toy is exclusively for Winter. He expands a photo of laughing Barnes and Rogers on the screen and waits for Jack to return.