I see this at almost all the Asian supermarkets in California, and saw it once at a Japanese grocery in Philadelphia. If you haven't had one before, I highly recommend it, although you might need help the first time, in order to figure out how to open the bottle.
The concept is that the soda is not actually carbonated, but the liquid is just highly pressurized. You open the bottle by pushing down a marble, which in turn releases enough pressure that bubbles form inside the liquid.
Not only are they fun to open, but they taste delicious as well!