This story is also on my other account on AO3, so no it's not a copy/been copied. Severus was with his group of Slytherin 'friends' that people just generally disliked. They were destined to be death eaters, to have a prejudice view. Avery and Mulciber had already hexed 7 muggleborns altogether just for having that blood status. Snape found himself in a predicament when he came across his group having some 'fun' with his best friend, Lily Evans, a muggleborn.
He watched it like a vivid, terrifying horror movie in slow motion. One of them raised their wand to her neck, no doubt about to utter the word 'crucio'.
"Stop!" He remembered shouting.
They looked back in surprise, anger. "Snape, this... this thing is a mudblood-"
"-and doesn't deserve any mercy." Another one finished.
Lily looked at him with hope, he could see a hint of happiness in her eyes. She was saved from that horrid curse, her best friend saved her. She was so grateful, she could hug him-
The other Slytherin's must've had a murderous look on their face as Snape stuttered, "that's right, she's a- she's just- just a... mudblood."
Lily's heart shattered, no, her entire world crumbled. She had made excuses for this boy, hung out with him and protected him, and he didn't even have the decency to do the same for her? In her outrage, she hadn't even noticed the tears stray down her cheeks, she hadn't even noticed the group of Slytherins, because that's all they were, Slytherins, cower back and watch her explode, screaming and anything around them shatter into minuscule pieces. But what she did notice was Sirius. He had hexed all of them and they stayed away for enough time for him to take her to somewhere more private, for her to calm down.
She knew Sirius hadn't been there to see what exactly had went down, but gathering that Snape was there with his group, she knew he knew it involved him.
Sirius didn't even have to ask her before she said, "Snape called me a mudblood."
"That son of an ugly bitch, I can't believe-"
"It's okay, Sirius. I should've seen it coming the day he was sorted into Slytherin."
"Eva-Lily, if you ever need me to hex him, come to me or James and we'd be happy to do it."
"Oh you don't need my permission," she managed a small smile.
Sirius had told James what had happened. And it was an understatement to say that James was vexed. He had marched up to Snape the second he saw him, and everyone watched in curiosity as they witnessed the rare look of complete anger and hostility sitting on his face.
"How dare you, Snape." Was all he everything but whispered.
Snape was terrified.
"Answer me." He said, then shouted, "Answer me Snape!"
Snape didn't answer, finding that the wrong thing to do, as he was hexed and jinxed into an oblivion. He didn't fight back. He knew he deserved this.
Later on in the common room, Lily approached James.
"James, I just wanted to say... thanks. I was wrong about you." She smiled and James nearly passed out with joy.
Now a few months later, James had finished his last detention, and Severus lay on his bed, regretting the moment he called Lily a mudblood.