Though not a traditional Japanese dessert by any means, ice cream has become quite popular. But, like most things, it's not quite the same as what you'd find in places like the US or Europe.
Ice Cream in Grocery Stores
Since grocery stores in Japan tend to be a lot smaller than the ones in the US, they have a smaller selection of many things, ice cream included. Haagen Dazs is pretty popular but it's the only US ice cream brand to be found in Japanese grocery stores and it’s significantly more expansive here. The most interesting things about the ice cream in Japanese grocery stores are the flavors and the size. I'll get to the flavors a bit later, so for now we’ll talk about the sizes. In a US store, most ice cream comes in pints with a smaller selection of larger and smaller containers. In Japan you’ll only find a handful of pints and usually in just a couple of flavors (vanilla and maybe chocolate, mostly). Instead, you'll come across a whole lot of little single serving containers that hold somewhere between 1/4 - 1/3 pints in a wide variety of flavors. I've yet to see any ice cream containers in Japan larger than a pint so if you can't live without galleon packs of ice cream you probably shouldn't visit Japan (and you should seriously consider changing your diet).
Ice Cream Stands & Parlors
I've seen a lot more ice cream stands and shops in Japan than in the US. Occasionally you'll come across a Baskin Robins and Japan has at least one or two Cold Stones as well. They’re both pretty similar to their US versions, though with a few flavors and toppings you won't see in the States (more on that in a moment). US chains aside, you'll see a lot of booths and small cafes selling ice cream (or sofuto kurimu (soft cream) as it’s often called). Said ice cream is always soft serve (so it melts pretty quickly in the summer), almost always comes in a small cone, is pretty much always the same size, and almost always costs 200 - 300 yen (around $2 - $3). Depending on the particular stand, there can be anywhere from one (vanilla) to about fifteen different flavors, with the average being around 4.
Ice Cream Flavors
Vanilla is the big one, just like in the US. If there's a place selling ice cream in Japan you can be sure that vanilla will be one of the flavors. Various types of chocolate are also popular as are the typical fruit flavors (especially strawberry). However, they really aren't the most popular. As I said, vanilla is everywhere but some of the most common flavors after vanilla are matcha, azuki, and melon. Mango and blueberry are also fairly popular. But, while those two sound normal enough, but I don't recall seeing a lot of mango or blueberry flavored ice cream back home.
To clarify, matcha is green tea. Haagen Dazs released their excellent matcha ice cream in the US a year or two ago (though it was out in Japan for years before that). If you’re in Colorado, Boulder Creamery also has a milder and creamier green tea ice cream that’s not too hard to find.
Azuki are sweet red beans that are used in a lot of Japanese sweets, particularly anpan (bread filled with azuki paste) and various other little bun, ball, and pastry type things. They taste like a sweet bean (kind of hard to describe if you’ve never had any) and can take a bit of getting used to, though most of my American friends who have tried various azuki based sweets ended up liking them.
While you can get several types of melon in Japan, if someone just says melon (as opposed to watermelon, for example) you can be pretty certain that they're talking about musk melon. Musk melon is a type of Japanese melon that’s pretty much impossible to find in the US. The outside is green and has a similar texture to a cantaloupe. The inside is green as well and tastes like a mix of a honeydew and a cantaloupe. As much as I like the actual melon, I don't think it makes a particularly great ice cream flavor, but that's probably just me. I love fresh melons but I've never really liked melon flavored things...
Anyway, those three (matcha, azuki, and melon) are the most popular flavors after vanilla and even American brands like Haagen Dazs and Baskin Robins have them here. But that’s only the beginning. See, nearly all of those soft serve ice cream stands stock the same brand and said brand has somewhere around 100 different flavors. A lot of stands stock or one two (or if you’re lucky ten or twenty) flavors beyond the basic and this is where things get really interesting. You’ll naturally find flavors for about every fruit imaginable, including some you may not have heard of before like ume (Japanese plums). There are also flavors for all the most popular teas, nuts and seeds (including unusual ones like chestnut and black sesame). And then they start to get odd. Flower flavors like rose and sakura (Japanese cherry blossoms) are rather mild but usually taste pretty good. And the ones based on various Japanese foods (many of which you normally wouldn’t associate with dessert) like tofu, rice, soy beans, and satsumaimo (Japanese sweet potatoes) aren’t bad either.
Finally you get to the really weird stuff. Wasabi ice cream, anyone? Can’t say I’m a fan (I did try it, twice in fact), but it’s great for a practical joke (just tell your friend it’s green tea). And the milder version is fairly edible, though I couldn’t even make it halfway a cone of the regular, and I like wasabi. But if that isn’t strange enough, you can also keep an eye out for flavors like snake, eel, and squid ink. Note that even to Japanese people, these really weird flavors don’t have much appeal beyond their novelty value so they can be pretty hard to find.
While I’ve ended up with a couple of ice cream flavors I wasn’t too fond of (like wasabi), most of them are pretty good, no matter how strange they may sound. And, worst comes to worst, at least you’ll get a good story out of the whole experience. So, if you’re even in Japan, take a look at any ice cream stands you pass and be adventurous. You never know what flavors you may end up liking.