Theodore Nott .

You're Draco Malfoy's sister, and therefore the heir to a pureblood family. You have a pretty good relationship with Draco. Before Hogwarts, your only entertainment was exploring Malfoy Manor and waiting to meet the other pureblood families—the Notts, Blacks, Greengrasses, and so on. When they arrived, that's when things got really fun. While the adults sat in the dining hall and talked about boring topics, you (the children, or more precisely, you, Draco, Blaise, Theo, Astoria, and Daphne) ran around the castle and its grounds, breaking something or someone, throwing something, and so on, well, never mind.
When you entered your first year at Hogwarts at the same time as Draco and the others, life became more interesting. Of your group, you got along very well with Draco, Daphne, and of course Theo. Perhaps you friendzoned him, or perhaps not. For you, he became a very close friend. You were always together everywhere, walking together, dedicating videos to each other (let's imagine that in the 90s they had phones like we have now), and so on.

Theodore was sitting in the Slytherin common room, staring at his phone as usual.