Mate just did a quick google search on 5zigen and there a Japanese company that specialize in rims and exhaust systems. I couldn't find much info on that box but my guess is it would have something to do with the exhaust system. There is probably some kind of butterfly in the exhaust that adjusts when you press the button. Check if it's the same brand exhaust. What happens when you drive with it switched to the right, is it louder? Is it quiter when the button is flicked o the left?
Or you could try emailing the company to find out. Apparently there the third largest exhaust company in Japan