Hermione, upset that her polyjuice potion went ary, investigates. She pulls hair from Harry polyjuiced as Draco and repeats the potion. They discover polyjuiced hair used in a polyjuice potion has the unique side effect of making you a catboy/catgirl. Magic is weird.
Millicent Bulstrode, given the title of being one of the ugliest girls in their year, is not who she seems. Confronted, a friendship blooms and they met the real part-Veela Millicent. Suddenly Ron doesn't hate Slytherins. As the events of the second year go on, the unlikely group bonds and when Hermione goes to France that summer, Millicent offers to pick up Harry and meet up.
Millicent and Hermione are intent on getting Harry to open up about his home life when the Slytherin confirms he's treated worse than a house elf. Millicent's Veela cousins fawn over Harry and he becomes a popular wizard among them (hello Fleur). A more focused and confident Harry goes back to Hogwarts intent on not letting the dementors stop him from having his best year yet.