The Second Captain

As far as the Avengers are concerned, Steve Rogers -a.k.a. Captain America- is an only child.
Except he isn't.
Steve has a little sister who was too young to really remember him, especially since he was always running around trying to join the army. In Morgan's eyes, he just wanted to get away from her, as far as possible.
When the Captain goes down with the jet, Morgan finds herself in an orphanage in an old part of town until a terrible accident occurs and she comes out as the sole survivor.
Now, almost 70 years later, she's grown up being cared for by Peggy and lived dealing with the side-effects of that incident.
How I wonder will Steve take finding out that the little girl he knew doesn't look as old as he expected?!
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This may or may not be mature and could probably go anywhere when it comes to love interest but I have no idea yet so yeah.... Its most likely gonna be a Loki or Tony fic but I havent decided. Well, I hope you like it!
P.S. Morgan's full name will be revealed in the story at some point but I dont know if I'll weave it in or just make a profile thing. Also, there is more to what happened in the past which will also be revealed in the story so please be patient because its hard for me to keep on it so read and rate and comment so that I update! XD