Stucky's lost daughter (LokixReader)

Prologue backstory

Y/N was laying at her bed, thinking about her first day of school. What will it be like, or do they will even like her at all? Can she make some friends or do they think that's she is a weirdo? So many question at the same time are constantly roaming through her head.
She was very smart for her age, she already knows how to read and write. Well that's what you get when you were born, or better to say made a super soldier. She also spends a lot of time with her uncle Tony, that's why she adapted a bad behavior and a special taste of music. Her favorite band was called AC/CD and her all time song was Highway to hell. Of course she listens to other music due to the fact that her parents are from the 1930's but that doesn't mean she couldn't love other styles. So the mix of these two types of music makes her style quite different from other kid her age. She would either dress up as a princess, but the too girly ones in big dresses or like some old metalhead with an old t-shirt from the 90's.

In the meantime her dads, Steve and Bucky are sparing at the gym while Clint was hiding in the vents. Nat was on a top secret mission. So y/n knew that's she wouldn't be back in just a few days. Usually these types of mission would take a week or more. Tony and Bruce are in the lab and building some kind of tech and stuff.
Everybody was doing their daily routine when suddenly an alert went off. 

A armed team of hydra agents stormed through the window. The tower immediately went into security mode. All of the Avengers were notified that intruders are moving up to y/n's rom.
The fact that they are already suited up for practice makes it easier to act.

When they reached her room they were shocked. They saw six HYDRA agents trying to grab y/n. She was fighting back all of them but failed. She screamed 'dad! Help!' from the top of her small lungs but that didn't work. They just gripped tighter and didn't let go of her. They immediately started to fight back in order to get their precious little daughter back.
Steve threw his shield at one of the agent's and disarm him. Bucky uses hand to hand combat to fight of 3 agents. He was able to put them down as more agents came in and grabbed him. Ironman shoot a whole magazine out of his hand blaster and kills most of them.
Y/N was hiding behind one of the chairs, suddenly one of her dad's guns slides on the floor all the way down to the little girl. She picks it up with shaky hands. She has never used one before, only saw her papa practicing with it, so she instantly knew what she had to do. It was heavier than she expected it to and even though she hates killing, this was a life or death situation. When one of the agents approached her she pointed the gun directly at his face. "St-stay away from me or I will kill you" she yelled at him. He just laughed and walked even closer. The agent tried to grab her arm and pull her with him. She kicked him in his stomach and stumbled a few steppes back. She again yelled at her family for help but they are also trying not to get themselves killed. Plus a dozens agents are blocking of their way to her. She yelled again and told him to back off so there was no way out for her. She repositioned the gun in her hand, pointed back at his face and pulled the trigger.
The bullet went strait through his skull and killed him instantly.
She was shocked that she had just killed someone that she completely forgot her surroundings. So she didn't notices that one of the agents gabbed her from behind and her a put a dump cloth over her mouth. She tried her best to fight him off, but only a few seconds later the world goes black and her unconscious falls limb into the agents arm.

Right after that he gave the signal to his fellows to go back to the base and all of the agents disappear as  fast as they came. Twelve hours later they arrived back at the base and put her into a cell. The only think that Y/N doesn't know is that she isn't any longer in the US. She is in a HYDA base in Germany.

The next day she was woken up by a bucked of ice water that was dumped over her head. She shoot up und dashed to the right corner of her cell. She slowly became aware of her surroundings and realized where she was.
The floor she was sitting was could as slightly wet. The floor and the walls are made of some sort of stone or even cement. There were no windows, from which she could have escaped. A single already muddy looking mattress was laying at the floor, other than that the room was empty, only a single light bulb was hanging down from the ceiling.Y/N started to hyperventilate and was close to passing out. When she was about to pass out a soldier came to her room, without any warning and named several rules that she to follow otherwise she will be punished. The rules are train everyday, learn the language German and Russian and never, never talk back...  She was to scared to talk back. She decided that she will follow the rules because she doesn't want to find out what will happen to her when she misbehaved. Probably the hardest part of these rules were the languages. She doesn't understand any word they are saying to her if they didn't speak English. So she hopes that the punishment for this wouldn't be too harsh.

The next thing she knows ist that six armed soldiers came to her cell, grabbed her and bought her to a scary room. In this room there was a machine that has a lot of whites attached to it. A table with restraints attached to it stands in the middle of this white room. Right behind y/n and the soldiers are scientists entering the room. They greeted each other and exchanged some sort of information in a language that she doesn't understands. Than without any explanation or warning the soldiers strapped her onto the table right in front of the huge machine.The straps are so tight that they nearly cut her wrists and ankles as she tries to get out of them.

A friendly looking scientist with a withe coat is now standing right in front of her. Y/N asked if this is going to hurt her with tears in her eyes. He didn't say anything, just started to smile evil and laugh. He said that this will hurt a lot and she slowly start to cry. They pushed a few buttons and the engine started to move. Some metal parts are now attached to her tiny body and are sending shocks right through her bones. Her head was buzzing from all the pain and so was her entire body. The shocks got worse and after only one minute of that torture, she fainted.

Y/N regained  conciseness and realized she is in a cell, her whole body felt numb and her head is spinning and buzzing. When she tried to remember what happens to her, she realized that she couldn't. Her mind was empty, there are no memory either happy or sad ones. Even thinking of something that should be easy to remember or hard to forget like her name or how she came here seems impossible. She didn't know where or who she was, all she knew is that her entire body hurt like hell. Her small wrists and ankles are still red and sensitive from some kind of rope. After hours of trying to remember she fell as sleep on the cold, wet mattress next to the dirty wall.

The next day she was woken up by shouting from lots of men. Awake and scared she started to look around. Her cell has no window only door has a small window to look through. There where is no bed inside, just the mattress she was currently lying onto. Other than that it was an old, cold room.

After what seems like houses a man with a angry look on this face came to her cell. He started telling her something in a foreign language that she can not understand. When she just looks blankly at him he hit her in the face. She was about to cry when he switched to English and started from the beginning in a pissed tone. He explained that there is a reason why she can't remember anything is that has happen when she was out.
According to him she doesn't have a name, only a number, she is called test subject 037. Right after that she was bought to a clean room that has lots of medical stuff like scalpels and needles, all of them in different sizes and what she thought various procedures. Behind that there are small bottles with colorful liquids. Some are see through others are yellow or in a bright blue tone. She was mesmerized and terrified at the same time.
A man with a white coat entered the room and escorted her to a table. He told her to lay down on her back and she obeyed. After that he strapped her onto it so tight that her limps almost went numb.
He said that he was going to have some fun with her, then picked up a large syringe and a bottle with a blue liquide inside. He sticks the needle into her arm and she screamed with pain. Over the next hours he continue to torture her, at some point she thought she was going to die or that was what she hoped for.

The next day she woke up on the cold floor, she started to cry when she looked down on her.  Cuts and bruises are located all over her. Just by looking at it the memories of the last day floated inter her brain. She curled up in a small ball and cried until she started to feel dizzy. A soldier ran into her room and ordert her to stand up, she did as she was told even though she was too weak to stand, due to the lack of food and water.

The hours went bye and the torture called training she was experiencing was exhausting. That's how the days went bye. Everyday was the same wake up, train and get experimented with different stuff, than crying until she passes out. When she talked back what she did more often she get punished. The punishment was pure torture for her, this weird scientist that always slimes sympathetically at her was he worst. He had some fun with her that means he stick or cut her with some sort of knives or scalpels.
As the years go bye she started to change, not only her appearance but also her mindset changes dramatically.