Then again it seems the show itself seems too concerned about flat chests; I'm surprised that Kaori got as much time as she did.
She strikes me as more "normal but shapely" as she seems a bit plain compared to more exotic girls (Hyouka, Kaori,etc.), but I think that's part of her charm.
Now I didn't read the novels (guilty), and didn't finish Index2 (don't ask, it's complicated) but I'm surprised that from what short time I've seen her, I could immediately recognize Fukiyose from the thumbnail. I think it's the shape of her face really, and that all-too-common pissed off look. So much for that "2D girls all look alike ha, cha cha cha cha~" that no one ever heard again.
Whatever though, I think one of the subtleties I love about these series because they give us lots of girls without giant tits exploding in your face, not that I mind one on occasion. It just feels tired when the industry thinks that's all people care about. There are plenty of reasons why flat-average-prepubescent bodies are appealing too though, unfortunately however, sometimes even THEY can come off as overbearing and pushy with the 'lack-thereof' of chest...