You know, sometimes the things that hate each other the most, that are the most sworn enemies are actually more alike than possible. Like Gryffindor and Slytherin. Harry Potter was almost put in Slytherin though he's a true Gryffindor. It was proven when the Sorting Hat decided to put him in Slytherin but Harry begged him not to, so the second choice was Gryffindor. Also when Harry got Godric Gryffindor's Sword. They're two sides of the same coin. Being Gryffindor Brave is to Slytherin Clever. Lion Loyal to Slytherin Sly. They're evenly matched up, neck in neck no matter what. They're Light and Dark but they all too much the same.
That's also what Rose Weasley and Scorpious Malfoy are. Two sides of the same coin. She's, as expected, the Gryffindor Princess while he, as expected as well, is the Slytherin Prince. Both with tempers as forces to be reckoned with. They were arch enemies but only because that's what the world expected them to be. She beat him in everything, but barely.
She was the model student. Straight O's, prefect, Head Girl, chaser on the Gryffindor Quiditch team, and all-around likable person. He was just the same. Straight O's, prefect, Head Boy, Seeker on the Slytherin Quitditch team, and opposite to everyone one in his family, so in short likable.
But the duo were always in opposite friend groups, on the surface they didn't have anything in common but their academic competiveness.
No one thought that when Rose, dear rosie, was secretly seeing Scorpious, that day, in a muggle fair that Aunt Hermoine just happened to want everyone to go. Boy, were they surprised when they saw them, wrapped up in each other in their little world. No one saw that coming.
But in their coming years, when everyone thought they'd break it off, they went on stronge. When they thought the duo were too weak, they became stronger. They were puzzle pieces, fitted together perfectly. Better for each than anyone else could.
And against all odds, they loved, lived and laughed till their days became old, and happy and they had no more.
Because she's Rose and He's Scorpious and they're not supposed to work. So that's why they did.