I generally don't waste calories on Japanese desserts because they aren't dessert-y enough for me. A tiny wheat roll with a squirt of bean curd in the center isn't my thing. But I am starting to get into sweet potato stuff. Potato cookies are great (not sweet, but they have kind of a creamy texture) and sweet potato ice cream (beni imo) is great. I can't really describe what it tastes like. Maybe vanilla but yummier.
I found this advertising poster in a Blue Seal ice cream store in Okinawa last weekend. It's a crap photo taken with my cell phone, but if you look closely you'll see that they're advertising three different types of potato ice cream . . . and each scoop is resting in a hollowed out potato skin! Delicious and tempting!