AN: This is not actually a completed story. This is just the semi-detailed plot. Sort of like a list of head canons. If the grammar or English is incorrect, I apologize in advance and hope for the understanding that this is just me jotting ideas, not an actual story.
Avengers (1)
Emilia (Emily or Ems) Cassidy Stark is Tony's daughter. She has a photographic memory. Her mother was an Inhuman. When she's 13, she's exposed to terrigen. She now has the ability to manipulate materials to build technology and communicate in any language (speech, sign, computer, etc.), as well as accelerated healing. Hydra discovers this and tries to capture her. Unable to do so, they threaten the people she cares about, and she runs away to protect them. She already knows everything she needs to in order to graduate high school and get her associate's degree, so she gets her GED and privately meets with college staff separately to arrange to take the tests without taking the courses (still paying for them, of course). She builds and repairs things for money and studies, getting the rest of her degrees the same way as before. She gains PhD's in Electrical/Mechanical/Biological Engineering, Biology, Biochemistry, Chemistry, Mathematics, Military Science, Physics, Psychology, Computer Engineering/Science, History, Mathematical Sciences, etc. (full list . ?az=all) by the time she's 20. She is a master of disguise and an absolute genius (from both powers and the Stark brains), so Hydra can't find her. She decides to work for S.H.I.E.L.D. (Secure Homeland Intervention, Economics and Logistics Division) and goes directly to Fury. She makes a deal with him that if she can keep her identity completely and totally hidden, she'll use her abilities to help S.H.I.E.L.D.. She's known as Agent Rosita Enly, Level 7. She's a fantastic fighter. She regularly spars with Natasha, and then Steve as a method of therapy for him. When Loki attacks, she's asked to come aboard the hellicarrier to find the cube. She befriends Banner, chats with Steve, and spars with Nat. When Thor, Loki and Tony arrive, she tries to stay out of the field of vision, but befriends Thor. During the argument, she stays in the back, not speaking, until an alarm goes off, and it gains all of her attention. She forgets that she's trying to stay hidden from Tony and rushes to deal with the issue. Tony sees her and does a double take, but doesn't have time to elaborate his thoughts, because the bomb goes off. She rushes to fix the engine, Tony and Steve right behind her. Seeing that she's unable to reach the spot she needs to get to, she uses her powers to make a flying glider (like the green goblin, but shaped like a skateboard). Steve sees her powers for the first time, and she flies off, telling him to make his way over to a certain spot. She meets Tony on the way there, who sees her, and says, "Do I know you from somewhere?" knowing she looks a great deal like his daughter (her image is burned into his mind). She shouts "Probably, but we can discuss facial recognition later! We need to focus on the task at hand!" so he puts it out of his mind for the time being. There's repairs that need done, and she keeps finishing his sentences, and she uses her powers to fix the problem, and knows Tony can handle the rest, so she flies away to help fight. She and Thor run together and find Loki right when he's coming out of the cage. After Thor's trapped, Loki advances on Emily with his scepter. He stabs her leg when she's sitting against the wall, and says that her abilities would be of use to him, and that she's a great warrior who could rule at his side. She spits in his face and he puts his scepter to her chest and tries to change her, but all that happens is slight second-long discoloration around the edges of her eyes and her wincing, and she's in complete control of her mind. Coulson comes in, Loki tries to stab him, but Emily knocks it out of the way. He blasts her, knocking her against the rail, and stabs Coulson. Loki drops Thor, and Coulson shoots him. Fury comes in and calls for medics. Steve rushes in as they're moving Coulson and Emily onto gurneys, Tony close behind. Coulson's dead. As they're moving Emily, she grunts painfully. They try to roll her into a better position, and she screams. The impact against the rail broke her back. They rush her to medical, Steve and Tony following until they actually get there and aren't allowed inside. Tony leaves first, goes to his lab, and has Jarvis search her files and get info. Jarvis reveals two identities, one by name forged by S.H.I.E.L.D., and the other by advanced facial recognition, revealing her to be his daughter. Tony's in shock, and sits, blankly staring at the screen. Natasha comes in, sees the screen, and talks to him. After awhile, Tony goes to where Coulson died and Emily got hurt. Steve finds him there. They talk. Medics call them in, they rush over, and a medic tells them that what's happening with Emily is astounding/shocking. She's been conscious the whole time, rejected pain meds, refused to let them use their machines or do anything but bind her leg. Even with this, her leg is nearly completely healed, and her back is such that it's as if the only damage was cracked bones. This shocks Tony, but Steve already knew. The medic tells them they should probably wait until she's completely healed to talk to her. Tony roams the hall, and eventually sits on the floor about 10 yards away from the door, which Steve remains barely 3 feet from. 20 minutes later, she walks out, completely healed, and hugs Steve, who tells her to try to not scare him like that again. She chuckles and says she'll try. They talk and walk in the opposite direction from Tony, who watches them from his spot on the floor. He sits there for a little while, then goes to fix his suit to get his mind back into focus. Steve and Emily talk while getting ready. They all head to New York. Using too much power exhausts Emily, so she prepares a bunch of gadget-throwing-knives and a spear and uses those. In the short version of the fight, she fights Loki and kisses Steve. She's far away from the Avengers when Tony directs the nuke, tells him godspeed over the ear com. When the Avengers head over to the Tower to deal with Loki, she makes a glider to fly over there. They all look up at her when she enters. She heads over to Tony (fast walk, then jog). He sees her coming toward him and steps out of his suit, and she throws her arms around him, sobbing quietly. She tells him "don't you ever do something like that again! I left to keep you safe, not so you could do crazy stuff like that!" in a shaky, sobby voice. He hugs her tightly and says "as long as you promise not do do something equally crazy, like run away again" in a shaky voice. Tears appear on both their faces. She says, barely above a whisper, "te amo papá," (I love you, daddy) to which Tony responds with "yo también, mi bebé" (me too, my baby girl) and a slight chuckle. Clint and Bruce (who by now has changed back) speak Spanish and raise their eyebrows in surprise, Bruce's jaw dropping. Natasha already knew, so she just smiles. Thor quietly asks what's going on, and Nat says "family reunion". End scene.