Images from Suntory.
During my long and far less than illustrious life, I've heard a lot of theories as to why people catch colds. The most common one, and in my opinion erroneous one, is that it happens when you get cold. Another is that you catch it from germs passed along. This is the one I believe, but I believe it only happens when your immune system is compromised or suppressed somewhat.
This can be caused by many things, but often happens when the homeostatic state of your body is severely disrupted by abrupt weather changes. I think the reason people think cold weather causes colds is that the shock to the system of a switch from warm to cold weather suppressed the immune system and people succumb to germs they might otherwise be able to fend off.
In Japan, Suntory talks about the threat to health should you allow yourself to become too dehydrated. They may have a point. I'm not certain, but it wouldn't be too far a stretch to say that dehydration also could suppress the immune system. Of course, they recommend you hydrate with their beverages including their Green Dakara drink. It's got green tea, vitamins, and minerals to help strengthen the body as well as moisten those vital tissues.
However, just in case drinking the Green Dakara won't do the trick when it comes to fending off colds, you can avoid inhaling the germs entirely by donning the free mask they'll give you with purchase. Whatever the risk, Suntory is doing its best to look out for your health. It has nothing to do with selling their drinks. No, sir.