Kitagawa is a piece of work indeed, thought I think even before Sone appeared in the story, Kitagawa started to change his ways somewhat. I mean, he did praise Nishimura during the sports event when she and Umi where gathering the balls for the basket throwing game.
He does have a long way to go still, but at this point in the story he's already a better character than Kasahara's (former?) friends, right?