Requested by @luna-D-umbreon and I hope you enjoy :)
You grew up in the Red Room with them both, Natasha and Yelena and you guys surprisingly became friends almost instantly
After taking down the Red Room, you had to tag along with Natasha and Yelena since HYDRA already ended up killing your parents and besides, they didn't want to go anywhere without you. Yep, your two best friends were under the delusion you were one of them, well... it's more a deep and dark twisted obsession
It started when they'd see you training and fighting in the Red Room along with them. Wow, you were so strong and agile, and quick on your feet. Your fighting movements were that of a swan, and they could see why you were one of the prized pupils there. Yelena was the first to have those protective feelings for as she saw you get beat up by someone. She immediately pulled them off of you and told them to leave you alone and you thanked her, which fueled her instincts to protect you even more
Speaking of danger, whenever you'd get assigned missions Yelena would volunteer as well since she doesn't want anything happening to you. What if you get hurt? She has to be there to protect you even though you're one of the Academy's prized pupils and skilled warriors there. And as for Natasha, she'll start growing big sis feelings for you as well sooner or later
But when she saw that smile of yours and as you kicked one of the people there like a pro, she thought you were amazing and she was starting to feel proud of you and yet scared for you at the same time. You were so young, you still had a lot to live for, not spending your life training to become an assassin, she feels bad for what happened to you
Surprisingly both of them came to a mutual understanding and agreement and they decide to look after you since they don't want to fight each other and plus, you'll have two strong and yet deadly assassins looking after you and protecting you for the rest of their lives, congrats, you have two deadly sisters who are now looking out for you
You guys finally escape and when you do, you'll get a safe house and from there their yandere tendencies will start showing in full colors. They don't want you going out since you could be wanted by SHIELD and who knows what other organizations are after you and they don't want you being caught. They'll be the providers for you don't you worry your pretty little head. And if you refuse to spend your time with them that wouldn't be a really smart move for you since as strong as you might be, they're more stronger than you and facing two stronger assassins than you isn't something you shouldn't be doing when you're being kidnapped by them
I'm sorry this sucked, I didn't really see the Black Widow movie and I don't know much about Yelena, I'm so sorry TvT

BINABASA MO ANG
YANDERE AVENGERS ONESHOTS
FanfictionEver wondered what the Avengers or the characters of the Marvel Cinematic Universe would be as yanderes? You'll get to know only if you read 'em. Hope you enjoy and none of the art which I use here belongs to me, so credits to the respective artists...