well first it was an attempt to emulate her in an attempt to catch mizu's attention and interest now I think its finally dawning on Kimura that someone so elite whom she had thought was above her and superior to her in every way can actually like her see her as worthy of giving attention to and that Hiyama is capable of being open with her feelings something that Kimura constantly struggles with. While yes this may at best hopefully be progress it could also be that Hiyama has merely inspired her and Kimura sees her as a role model of sorts.
Meanwhile Mizu is completely oblivious to this and I'm starting to believe he just sees the girls around him as those mob npcs from various animes and manga.