Okay, Nat doesn't have any superpowers. One would expect her to get kidnapped frequently, but she doesn't. This makes it a surprise when she goes out on a mission and never comes back.
The Avengers assumed she'd tired of them or something like that, but she had been kidnapped by HYDRA trying to reclaim their lost asset. They try to rebreak her by any means the filler deems appropriate. HYDRA does this rebreaking at the same facility as the Winter Soldier is stored at/they attempt to use the Winter Soldier to break her.
Of course, at some point, the Avengers realize that she was kidnapped and go looking for her. When they find the base she's at, they rush in to see a traumatized Natasha being guarded by a shaken Bucky.
+ If Natasha doesn't remember most or all of the Avengers. + If Bucky recognizes Steve not as his friend but as Captain America, his savior from Zola back in WW2. + If this happens pre-WS, so Steve had no clue that Bucky was still alive. + If it is implied this sort of thing has happened before by Clint. ("Oh. Hey James, I'm here to get Natasha again." **attack** "Okay, is it a Soldier day again? Good to know.")
The Time Hydra Kidapped Natasha
The Avengers assumed she'd tired of them or something like that, but she had been kidnapped by HYDRA trying to reclaim their lost asset. They try to rebreak her by any means the filler deems appropriate. HYDRA does this rebreaking at the same facility as the Winter Soldier is stored at/they attempt to use the Winter Soldier to break her.
Of course, at some point, the Avengers realize that she was kidnapped and go looking for her. When they find the base she's at, they rush in to see a traumatized Natasha being guarded by a shaken Bucky.
+ If Natasha doesn't remember most or all of the Avengers.
+ If Bucky recognizes Steve not as his friend but as Captain America, his savior from Zola back in WW2.
+ If this happens pre-WS, so Steve had no clue that Bucky was still alive.
+ If it is implied this sort of thing has happened before by Clint. ("Oh. Hey James, I'm here to get Natasha again." **attack** "Okay, is it a Soldier day again? Good to know.")