Your father is Severus Snape, your mother was Lily Potter, so you’re Harry Potter's half-sister. You grew up with your father and never met Harry. He didn’t even knew he had a sister. But you knew that you were his sister. You just never met him.

Since Severus was a teacher at Hogwarts, he often had to be there, except for the holidays and sometimes the weekends. But you’re still close to each other. When he was at Hogwarts, you always stayed at Malfoy Manor with Lucius (your godfather), Draco (your best friend), and Narcissa (basically your substitute mother).

harry is three year older than you. So is Draco. Draco and Harry are basically archenemies. Lucius and Narcissa always treated you like you were their own daughter. And Draco has always been very protective, possessive, and very affectionate over you.

now are summer holidays. you’re 9 y.o., wich means Harry and Draco will be in their second year at Hogwarts and are 12.

Lucius went with you and Draco to Diagon Alley to buy Dracos school books and the other things he needs.

harry is with the Weasleys and Grangers at Flourish and Blotts to buy their own books. Just after Gilderoy Lockahrt insisted to make a photo with Harry and he, Hermione, and the Weasley kids wanted to leave, Draco came down the stairs of the second floor of the shop. You were still outside with Lucius because you two got your wand.

Draco: “Bet you loved that, didn’t you, Potter? Famous Harry Potter, can’t even go into a bookshop without making the front page.”

Ginny steps in front of Harry and glares up at Draco.

Ginny: “Leave him alone.”

Draco smirks mockingly at Harry

Draco: “Oh look, Potter. You’ve got yourself a girlfriend!”

Harry glares at Draco, when then suddenly Lucius enters, with a girl (you obviously) clinging shyly to his hand

Lucius: “Now, now, Draco, play nicely.” he looks at Harry and smiles. Of course not a sincere smile. “Mr. Potter. Lucius Malfoy. We meet at last.” he introduces himself and politely and briefly shakes Harry’s hand.

then Harry sees a girl about 3 year younger than him shyly peeking from behind Lucius, clinging tightly to his hand. You. Harry asks himself who she might be.