Hulk
Bucky had certainly heard about the Hulk, one can't live in Avenger Tower and not know about him.
He's noticed the differences when the others talk about him, so far Bucky has only met Sam, Tony, Natasha and of course he lives with his Omega.
While Tony talks mostly of Bruce he has mentioned the Hulk as a precaution just in case something happens.
As for Natasha, she always looks just shy of frightened, if Bucky were any one else he would not have seen it, but Bucky half raised Natasha, he remembers her crying and crawling into his bed before he had to return her to her own, he sees her terror, no matter how well she hides it.
Steve talks about Hulk differently, there is no caution only words about how sweet the childish Alpha is, how the green fellow is large and perhaps a bit simple but still as much a person as anyone else is. His Omega makes Hulk sized treats to ensure there is one for him when they are done Avenging, just the same as all the others get.
Bucky thinks it's sweet and it does not surprise him as much as it probably should.
So when the green alarm goes off Bucky is not concerned, instead of fleeing like some of those that work in the Tower Bucky goes to find the Hulk.
He watches for a few moments as the large green man tears his way through the gym, like a child throwing a tantrum and alright Bucky understands what Steve means.
"Hey." Bucky says, he does not flinch when the other Alpha turns to him and growls.
In fact Bucky growls back, deeper and longer and he watches as Hulk looks down and away, like a scolded child, which is what he is.
"What's got you so bothered, kiddo?" Bucky finds himself asking as he comes closer.
"Hulk scared." Hulk muttered as he shuffled.
"Yeah, I get scared sometimes too." Bucky admitted as he sat down nearby.
The Hulk looked at him and moved closer and Bucky held out his arms and was only mildly surprised when the green man tucked himself into them.
Bucky shifted to get more comfortable but placed his chin on the Hulk's head when the other went to pull away.
"You're fine, Hulk, just adjusting, you're a big boy." Bucky assured the man.
"Protect puny Banner." Hulk whispered, "He not safe."
Bucky knew Banner was Hulk's other half, had learned that while Hulk was an Alpha Banner was an Omega.
"Did someone try to hurt him?" Bucky asked, feeling anger for the other man.
Hulk nodded slightly and while Bucky wanted to find out who he had a scared child in his arms to take care of first.
"You're such a good brother, protecting Bruce when I can't." Bucky said softly, because he'd seen the way Hulk had submitted, the other knew that Bucky was the head Alpha of their family, the one Steve had made.
"Hulk good?" Hulk asked and Bucky's heart broke because of the insecurity in his voice.
Bucky forced the big green man to look at him and smiled, "Yeah, Hulk's a good boy, but good boys need naps to calm down, why don't you go to sleep, I'm here, I won't let any one hurt you or Bruce, and when Steve gets down here I'll go take care of the guy that tried to hurt Brice, alright. You did the right thing getting him out of there." Bucky assured the man in his arms as he carded through his hair, soothing him down into sleep.
It took a few moments longer for the green to recede to pale skin and for the size to reduce down.
Bucky continued for a while longer before carrying Bruce up to the rooms he and Steve shared, he tucked him into the bed he shared with his Omega and watched the other man scent the pillows and relax fully.
He kissed the man's forehead and went to find out who had tried to hurt his child.
They would not do so again.
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A/n: well, technically this is Hulk's chapter, I want Bruce to have his own separate chapter.
And Bucky doesn't kill the man the hurt Bruce(said person was very much not taking no for an answer) but only because Tony and Steve convinced him that death would be the easy way out.
And well if Bucky starts searching Hulk out when code greens happen it's only fair that he spends time with his Alpha child when he comes out, and maybe they spar so Hulk isn't just destroying stuff in a temper tantrum.
Yes i place Hulk on a more juvenile level than he probably really is but how long has Bruce had the Hulk? I am going with an idea that Hulk is only actually a few years old, basically Bruce's accident was Hulk's birth and he's not as old as Bruce but he still has an Alpha's protective instincts and before Bucky no one even tried to understand and Bucky was basically shooting off pheromones that said, 'i'm your dad now, i'm gonna keep you safe' kind of like Steve did during the Battle of New York when he gave Hulk permission to Smash.
So Hulk listens and lets Bucky cuddle him and feels safe with him something he hasn't really felt, even with Steve, because out of all of them Hulk has always known that Steve is an Omega and therefore needs to be protected just as much as Bruce.