Black Widow wants Captain America's babies

While there is some sexual tension between the two impossibly beautiful superpeople, we're not talking about Black Widow locking down Captain America with an unexpected (and impossible) pregnancy. According to one theory, BW only wants some of that sterling Steve Rogers sperm for scientific purposes. She knows that Cap wouldn't willingly hand over his badass baby batter, so she's settling for the next best thing: For Steve to settle down with a lady and have a family. That way, SHIELD can do some covert research on the inevitable Steve Jr.,  potentially using those genetic traits to recreate the Super Soldier serum. That, and they definitely want that kid on their kickball team.

At the beginning of Winter Soldier, Black Widow is pestering Cap about finding a date. Flash forward two hours and one tradmarked Giant Marvel Sky Battle later, Black Widow is still on Steve to find the right gal.

We know that Sharon is a SHIELD agent, so she's probably in on the operation. She'll carry Steve's kids to term, and after the new genetic material is analyzed, Nick Fury can create the next generation of superheroes and proceed to yell at them. Black Widow knows this is a long-con, so she's not pushing Steve into anything. More like nudging.

Though she and Cap seemed to have come out of The Winter Soldier with a stronger connection, it's never a good idea to underestimate B-Dubs. As evidenced by the opening mission in Winter Soldier, she's proven that she's perfectly willing to carry out missions without the knowledge of her teammates.

As it turns out, Black Widow does have a superpower: Secrets. Sexy, sexy secrets.