Disclaimer: This is a fan work only, and no profit is being made from it. This disclaimer applies to the entire work.
A/N: I'm working off of a headcanon timeline cobbled together from the MCU and what I could find on various wikis about the comics. To put it simply Natasha is older than her file in the MCU indicates, but not as old as in the comics.
The first thing Natalia Romanova learns about her new instructor is that no one talks about him by name, or even by codename. The Red Room girls are told to refer to him as "Sir."
It makes it harder to exchanged whispered stories about him after lights out in the dormitory, but also makes speculation about him more exciting. The dormitory is monitored. Their whole lives are monitored, but they are accustomed to it. They are permitted a certain degree of normalcy in some things, to encourage the development of social skills, and thirteen year old girls gossiping after dark is one aspect of that permissiveness.
Natalia doesn't participate in the late night discussions. Her thoughts are her own, the only thing she can really claim ownership over. Why should she give them away?
Sometimes she wonders if she should feel guilty about her possessiveness.
Natalia would memorize the new instructor's face, if he ever took off the mask (The arm she dismisses as too easily to disguise or alter to be a distinguishing feature). She's been taught to learn faces quickly, whether of targets or allies, and it unnerves her not to be able to follow through on that training. She speculates that this is why he always wears the mask, to desensitize his trainees to this feeling, and she memorizes the combat techniques he drills the girls in. Every night, she goes over the forms in her mind. When she starts significantly outpacing the other trainees, he starts giving her additional training, private lessons.
She learns sixteen new ways to kill a human being in the first month of training with the new instructor. She also turns thirteen.
Some nights, after she reviews the day's training, she imagines what the instructor (he's not new anymore) looks like under his mask.
Two months after she turns thirteen, Natalia begins training in using her sexuality as a weapon: how to sway her (slim, slightly boney) hips just so, what to do with her hands when to distract even without touching, how to make her eyes promise things she doesn't really understand yet. Sometimes, she pictures a target for her actions. Sometimes, she pictures the target has one of the faces she has imagined for her teacher.
It has been three months since she began her private training when she defeats the instructor for the first and only time in the sparring circle . It shouldn't have happened. He's more skilled than her, stronger and faster than any skinny thirteen year old girl. There are no outside factors giving her an advantage, but she beats sweeps his legs out from under him and his head hits the floor hard. Before he reacts she has him in hold that would let her snap his neck even with her scrawny build.
It shouldn't have happened. His reaction times have been off by just a split second since the training session began.
He looks up at her, slightly dazed, and she can see a hint of a smile in his eyes.
"Good job," he says, in English. His eyes flash with confusion. "Good job," he says again, this time in Russian.
The last day she trains with him, she kisses him through the mask. She's been trying out her new skills on him all week in private lessons: the hips, the hands, the doesn't really understand what she's feeling, only that this man is everything she wants to be and he thinks she's worth private lessons. No one has made her feel special like this before.
He hasn't reacted at all.
At the end of that last session, he tells her she's done remarkably well and that one of these days she may actually be able to take him down when he's actually trying. It takes her a moment to understand that he's almost making a joke. Over the last few months he's loosened up in some indefinable way, but this is the most animated, the most human she's ever seen him.
She stands up on her toes and presses her mouth to where his lips must be under the mask. He freezes and then, very gently, puts his right hand - his flesh and blood hand - on her shoulder and pushes her away.
"You're beautiful, Natalia. Beautiful, smart and strong. Any man would be lucky to have you. But you're still a child," he says. It's the first time she's ever heard him say anything not directly related to training.
"And you deserve better than me," he adds, in English.
The next day, there is a new combat instructor.