One day, after purchasing his school supplies with Hagrid, Harry was making his way to use the bathroom before getting on the train back home. On his way, he had accidentally bumped into a girl, who introduced herself as Daphne Greengrass.
The two of them became friends on the train ride to Hogwarts, and despite the negative press Harry received from others about Slytherin house, Harry didn't let that interfere with his friendship with Daphne. Yes, Daphne became a Slytherin, and she had Slytherin traits, but only the positive ones. And Harry had to admit that he liked her traits.