While we wait: It seems like Haruko is an out-and-out lesbian who probably didn't think about what she was before she started kissing and socializing with Natsuko, but is happy about it. Natsuko is more romantic and maybe feels the need to have something with Haruko to justify kissing with her. Also, Haruko defers to Natsuko quite a bit. Yes, she's a brat, but a brat that accepts that Natsuko can keep her under control. Like Natsuko is in Romantic Two-Girl Friendship territory and Haruko is like "My God, actual girls, I want some! But I won't hurt Natusko's feelings by trying to jump her bones or her friends. For now." It seems like every time Natsuko makes her blush she turns her head away.