[godwine]

First ask yourself this question: Why does it have to be Japanese?

Girls can easily sense it when someone approach them with the wrong intention. There are definitely girls that looks for a fling of some sort, and will be more open to physical relationship with strangers, but these girls are not common, not in Japan anyways. You may find a few in bigger cities, but as Nyororin pointed out previously, these girls get passed around by foreigners. In Chinese, we call loose girls like these as "Public Bathroom"

Anyways, Japanese girls appreciate people, especially foreigner to approach them for the "right" reason. Right or wrong is a point of view, but in general, people tend to adhere by what is socially acceptable. Open sexual relationship is not socially acceptable in Japan, as such, if you walk in with just the intention to get lucky, that will not work.