[Nenkitsune]

I think Shimizu acted cold to him when they met at school because of the way she was raised. when she first met Nagi, he was simply a tourist, so she could have fun with him and act like herself since he knew nothing of the traditions. but once he became an islander, she had to stick to her traditions and the way she was raised. but now he's the dragon god, so it's ok for her to get close to him and act a bit like herself. something like that.