Staron

"'Sharon...so pretty...you...take my...breath' - Steve Rogers, Captain America #25" Staron is the het ship between Steve Rogers and Sharon Carter from the Marvel and Marvel Cinematic Universe fandoms.

Winter Soldier
Steve showed interest in Sharon and asked her out for a coffee, but she turned him down. Nick Fury gets hurt and Sharon helps Steve get him to a hospital and reveals she's an agent of S.H.I.E.L.D. Sharon calls him "Captain Rogers" and Steve calls her "neighbor", when they see each other again.

Civil War
Steve finds out Sharon is actually Peggy Carter's niece at Peggy's funeral and Sharon tells about her childhood and memories with Peggy. After the funeral, they had a nice talk about Sharon's spying on Steve to do her job and about Peggy. Sharon helped Steve as one of his allies risking her life to save him and his friends, she fought against the winter soldier and gave Steve and Team Cap his weapons and costumes back. Steve thanks Sharon for helping him and they shared a kiss before she goes.

Comics
Steve sees Sharon for the first time and realizes she looks so much like a girl he fell in love in world war II but he knows she cannot be her because she would look so much older, so he starts to follow her and they end up in danger together, the Captain was impressed with her abilities of fight, spy and intelligence and they become closer with her fighting at his side as his partner and biggest ally, she tells him who she is and who she works for and they fell in love in a intense passion but with arguments because he wanted her to give up on being an agent of S.H.I.E.L.D for her own safety and she refuses to left S.H.E.I.L.D and her job to spy, fight against the evil and protect the world, so many times Sharon was taken by Steve's villains and he runs desparate after her but when he arrives he finds out that it's all a plan of Sharon to infiltrate in the enemie's place and defeat them and that she could defeat them all alone with her fight an spy skills.

Then, Steve propouses to Sharon so many times but she refused because of a secret and she was keeping from him and no one could ever know, Sharon's sister Peggy Carter is alive and she was the girl that the Captain fell in love in world war II and Captain never found out her name.

Sharon and her parents tell the truth about Peggy to Steve, she was in the madhouse because of her mental problems and Sharon explains to him that the reason why she refused his porposals and broke up with him once was because of Peggy who was still obsessed with Captain America after all these years in the madhouse, Steve meets Peggy again and she recognizes him, however, he wasn't in love with her anymore, he loved Sharon, so he tries to tell her that the romance he had with her in the past was over, but she refuses to accept and cries everytime he asks her to not follow him on his missions for her safety, even with Steve's ask, Peggy still follows him everywhere and fight with her parents and with her sister Sharon when they try to stop her to protect her, at this time, Sharon and Steve got together in secret to not hurt Peggy.

After being controlled by Dr Faustus in a mission, Sharon explodes herself and everyone believes she was dead including Steve who gets hurt desparate for losing the love of his life.

After some years, Fury and Steve found out Sharon was still alive and that she believe Fury was the guilty for her abandonment and for the years that she had to spend alone to survive, she becomes a cold and angry person, Steve and Sharon start to work together again and provoke each other having a lot of arguments but hiding a sexual tension, but then, finally they understand each other and get back together untill civil war when Sharon is controlled by Dr Faustus and Red Skull and kills Steve, the last words of Captain America was "Sharon, so pretty, you...take...my...breath" and he dies leaving Sharon crying. Bucky Barnes take the legacy of Steve and became the Captain America until Steve comes back to life and him and Sharon back together.

Fanon
There're many comic fans who ship Steve and Sharon, although MCU fans disapprove the couple.

Trivia

 * Natasha's plot in the movie "Captain America: The Winter Soldier" was originally written for Sharon.