Summer in Japan usually has everyone breaking out the mugicha (that's barley tea for those who aren't living in Japan) but I've never been a fan of any of the cold Japanese teas. I find them all roughly inoffensive and mugicha would actually be my favored cold tea among what I consider the 3 "biggies" - mugicha, oolong tea, and ju-rokucha (a blend of 16 ingredients in an herbal tea) but I pretty much prefer western drinks.
When I get tired of diet sodas and want something with more frost to it, I turn to a frappucino. Since Starbucks is a fair distance away and their frappucinos are full of sugar, I wanted to work out how to make one on my own. I'm sure this is a lot easier to accomplish back home than in Japan because crushed ice machines aren't commonly included with refrigerators here as they are in the U.S.
The first step is getting the equipment which isn't all that hard if you can locate a blender which is powerful enough to crush ice. I've had really bad luck with blenders burning out on me after short-term use though. So, I decided to order the ice crusher/blender attachment for my Braun Multiquick hand mixer. The good folks at Yodobashi will order all sorts of extras for you if you tell them the part number and the attachment is listed in the back of the Multiquick manual.
The Multiquick mixer unit along with a whisk attachment and a small food processor bowl can be purchased at Costco in Japan or at Amazon Japan for about 6,000-8,000 yen. I can't recommend this mixer enough for its various uses and small size. It beats my old small food processor hands down and makes a mean smoothie.
For a low-fat,sugar-free chocolate frappucino, the ingredients are:
1/2 cup low-fat milk
1 tablespoon (soluble) cocoa powder (Van Houten is very good and sold at Costco and some Japanese supermarkets)
1 tablespoon low-fat powdered milk
1 teaspoon of pectin (sold in supermarkets near the gelatin under the katakana letters - pe-ku-chi-n)
3 packets of sweetener (I use Splenda purchased from the Foreign Buyer's Club)
dash of vanilla extract
dash of cinnamon
about 1 cup of crushed ice (about 6-8 Japanese cubes)
Put all of the ingredients except the ice into the blender and blend until it is mixed well. You should probably mix it for between 30 seconds to a minute to try and get the cocoa to dissolve and the pectin to thicken. Add the crushed ice and blend again for from 30 seconds to a minute until it resembles melted chocolate ice cream from the top (see picture below).
You can vary this recipe to make a coffee frappucino but be careful not to overdo the liquid relative to the ice quantity or all the ice will dissolve into the coffee and leave you with a coffee shake drink. Make sure you keep the ratio of liquid to ice the same (a half cup of liquid ingredients to a cup of ice). Also, make sure your coffee is very cold and strong if you use espresso and ditch the powdered milk but keep the pectin. In fact, I recommend you use 2 measures of ground coffee to one measure of water in your espresso machine to make it very, very strong and then use 1/4 cup of full fat milk and 1/4 cup of espresso as the 1/2 cup of liquid. Alternately, you could try the recipe above and substitute instant coffee for the cocoa powder although perhaps reducing the quantity.
All of these ingredients can be found in Japan relatively easily, particularly if you are flexible about brands. The hardest to find item at regular supermarkets like Seiyu or Ito Yokado is pectin. It is probably only carried by about 1 in 4 markets so you'll have to hunt around.
If you're on a diet and dying for something with chocolate, this will likely satisfy you with a very low caloric hit (about 70-100 calories depending on the milk type) and it's full of water so you feel full after drinking it.