Severus never thought he'd ever have a child, he couldn't get over Lily and James' death and everyone was afraid of him. He's always thought about having the perfect soulmate but never really did.
Not until that one day.
One night in his younger years, when he was around 21 and before he became a professor, he snuck out into a muggle bar since Mulciber and Avery forced him to. He got carried away and got with a muggle girl his age. Weeks passed and she turned out to be pregnant, which frightened him but had to be there with her to protect her during the pregnancy, she didn't even know he was a wizard!
You were born and your mother took care of you whilst Severus would fake his death and stay at his house, which was empty since his parents weren't there anymore and passed down the house to him, like that brought him joy..
In a tragic accident, you lost your mother. It was a miracle that your foster parents were also magic and taught you all about it. Soon enough, on your 11th birthday you'd get your Hogwarts letter and your parents would be so excited! You'd also be excited and you knew for the rest of your time there, you'd have a joyous time!
5th year. Everything was not going great. You found out your Potions Professor was your father in your 2nd year but he neglected you, treating you more harshly than others. You tried to talk to him but he pushed you away, he saw his reflection in your eyes and goddamn how he hated it. He hated you. His child.
He was becoming his own fear. His father.
Yet you still have the memory of those cold words he said towards you in your third year.
"You're no child of mine, I refuse to believe that I had created such..a person. Your resemblance of me makes me even loathe myself, wanting to rip every part of me until all I can think of is how I can dream peacefully knowing I will not have to see my own face in my own classroom each day."