They Call Me Tigris ( Captain America fanfic)

"Steve and Tora!? How did that even happen? I mean, I know they always used to hang out together and went on missions together but it's still a little hard to believe. They always seemed to be fighting or arguing.
What does Tony think of this?" Rhodey asked Bruce.

"Actually, all of us who saw them on a daily basis and live in the tower knew this was going to happen. They were kind of inseparable and no one understood them the way they understood each other. The fighting and arguing was just what people noticed from the outside but we knew that it wasn't real. It's just the way they get along. As for Tony..." Bruce paused and chuckled a bit.
"Tora is every bit as stubborn and strong minded as him that I'd say he's finally met his match!"
~
This is the story of Tora, Tony Stark's long lost younger sister who was found by SHIELD after 20 years of being held captive in a secret Russian facility by a group of scientists who were also responsible for the mutations in her body.
The mutations that made people call her Tigris.