I bought this at Banana Republic in Hawaii a few years ago, but I only wore it twice before washing and storing it. It's a US size XS, so I feel like it's closer to a Japanese size M, somewhere between a 7 and a 9. I usually wear a size 9, and while I can wear this, it's a little tight. It has a lining from the bust down to near the hem, so I think you could wear it directly without worrying about your nipples showing.