You were the godchild of Bellatrix Lestrange and she loved you like her own. Your “death” in the battle of Hogwarts destroyed her and the rest of your family
You save Draco Malfoy from the ice. He doesn’t know you’re the dark lords daughter but when he does, it seems he’s completely in love with you and isn’t afraid to show it.
Narcissa has lost all her family over the years. Bellatrix has become mad and drifted away from her, becoming obsessed with the dark Lord and Andromeda was removed from the family when she was only young. And her favourite sister (you) had disappeared years ago and had never returned. Everyone assumes you dead. Narcissa adored you. She was affectionate, possessive, obsessive, loving, docile, clingy and concerned for your health. You two were always seen together and Narcissa practically worshipped the ground you walked on. She would’ve done anything for you.
Last year Triwizard tournament was a disaster. You were presumed dead in the second challenge. But next year has come and Harry Potter kicks up to shore with the body of Draco Malfoys girlfriend (you)