I just really really want to rec this here (possibly again) because I love it so much.

Two for the Show by mousie tongue [ff.net]
[ Clint&Natasha | R | 31,000 words | high school AU | complete | warnings: physical and verbal bullying, sexualized assault, violence, homophobia and homophobic language, swearing, child abuse, implied non-con ]
After her uncle is taken, young Natasha Romanov ends up in state's custody at a group home. She can tough it out alone... but somehow fellow resident Clint Barton becomes the reason she doesn't have to.

And its sequal:
Upon this Winter's Night by mousie tongue [ff.net]
[ Clint/Natasha | NC-17 | 13,500 words | AU | complete | warnings: violence, swearing, sex ]
They aren't in high school any more: so why are they acting like two awkward kids staring across a dance floor at each other?

I cannot express just how much I love this verse (no really, I can't. I tried about four times and deleted each time). The AU aspects of this fits so perfectly with the characters and their canon/fanon backstories, I sort of want to roll around in its gloriousness. And even better, everyone gets a cameo appearence! And everyone is very much in character, despite the removal of much of their comics backgrounds. And it's just so good.

And please, be aware of the warnings, but also that the issues are well handled and not the main focus of the story.

Title: You Will Always Fall In Love, And It Will Always Be Like Having Your Throat Cut
Author: redbrunja
Characters: Natasha/Clint
Word Count: 400
Rating: R
Warnings: Sexual content, sexual slurs.
Summary: Natasha Romanoff moves like the flash of light off a knife blade.

Livejournal

AO3

Author's Note: Literally written at 2:30 a.m. Written for sugar_fey s prompt from Deathless by Catherynne M. Valente, "A farmer wants his son to be afraid of beautiful women, so he will not leave home too soon, so he tells a story about how one drowned his brother's cousin's friend in a lake, not because he was a pig who deserved to be drowned, but because beautiful women are bad, and also witches. And it doesn't matter that she didn't ask to be beautiful, or to be born in a lake, or to live forever, or to not know how men breathe until they stop doing it."