The mission was supposed to be routine.

In, out. Quiet. Clean.

Hydra had sent them to retrieve intel from a warehouse on the outskirts of the city. Nothing unusual. Nothing complicated.

Yet Bucky Barnes barely registered the mission itself.

His mind kept replaying the same moment over and over again.

Steve grabbing you.

Steve’s voice raised.

Steve losing his temper.

Bucky had been across the training floor when it happened earlier that day. You’d been sparring with Steve, doing exactly what he’d agreed to do—teach you how to fight without hesitation, without fear. But you were still learning. Still unlearning Hydra’s programming.

You hesitated.

And Steve snapped.

He’d grabbed your arm too roughly, hauling you upright, his voice sharp as he barked at you to stop freezing in the middle of a fight.

The room had gone silent.

Because Bucky had gone still.

He hadn’t intervened. Not then.

But the look in his eyes had made even Natasha take a careful step back.

Now hours later, the mission was nearly over. Natasha had taken you to secure the data while Bucky and Steve checked the perimeter of the empty building.

The hallway was dim, lit only by flickering fluorescent lights.

Bucky slowed his steps.

“Steve.”

Steve stopped walking.

Turned around.

“What’s up?”

Bucky stepped closer, boots silent against the concrete floor. His expression was calm—too calm.

“The next time you lose your cool with her,” Bucky said quietly, “I suggest you find a different approach.”

Steve blinked.

One eyebrow lifted slowly.

“Oh yeah?” he asked, crossing his arms. “Why’s that?”

Bucky’s face didn’t change.

But his eyes did.

Cold.

Sharp.

Deadly in a way Steve had only seen on battlefields.

“Because if you don’t,” Bucky said evenly, “it’s gonna put me and you in a position where things will definitely go south.”

The words weren’t loud.

They didn’t need to be.

Steve stared at him for a long moment.

Because Bucky Barnes had never threatened him before.

Not once.

Not in Brooklyn.

Not during the war.

Not even after everything Hydra had done to him.

But Steve could see it now — the line in the sand.

And he understood immediately.

This wasn’t about a sparring match.

This wasn’t about training.

This was about you.

Bucky’s partner.

His person.

The one thing Hydra hadn’t managed to take from him.

Steve exhaled slowly.

“You think I’d hurt her?” he asked quietly.

Bucky’s jaw tightened slightly.

“You grabbed her,” he said simply.

The hallway felt smaller suddenly.

Steve rubbed a hand over the back of his neck, frustration flickering across his face before it softened.

“I lost my temper,” he admitted. “She froze and I—”

“Don’t.”

The word was quiet.

But it stopped Steve instantly.

Bucky stepped a little closer.

Not aggressive.

Not loud.

But unmistakably protective.

“She’s already fighting a war in her own head every day,” Bucky said. “She doesn’t need you adding to it.”

Steve held his gaze.

And slowly… he nodded.

“Alright,” he said. “Fair.”

Silence settled between them for a moment.

Then Steve huffed out a small breath.

“You know,” he muttered, “you could’ve just told me to back off.”

Bucky’s lips twitched faintly.

“Did.”

Steve snorted.

“You threatened me.”

Bucky shrugged slightly.

“For her?” he said simply.

His voice was steady.

Certain.

Unshakable.

“I’d do worse.”

From down the hall, footsteps echoed as you and Natasha returned with the intel.

And just like that, the moment passed.

But Steve understood something now he hadn’t before.

If the world ever came for you—

It wouldn’t just have to deal with the Winter Soldier.

It would have to deal with Bucky Barnes.