Ah, tenmusu, one of my favorites. Basically, tenmusu is a little piece of tempura (天ぷら) snuggled away in a miniaturized nori-covered rice ball (おむすび). It is most famous in Nagoya, but available all over Japan.
Its popularity could be attributed to the fact that it’s a perfectly-balanced snack, with carbohydrates from the rice, protein from the shrimp, and vegetable goodness from the pickled coltsfoot (きゃらぶき) garnish usually served alongside. The special batter used on the shrimp stays yummy and crisp rather than wet and mushy for long periods of time, and tenmusu are easily eaten in under three bites, as well, making it ideal for those on the go.
More important than convenience, though, is taste, and tenmusu definitely are delicious. There’s just the right proportion of rice to keep the tempura, which is well-seasoned since the tenmusu isn’t served with sauce, from being overpowering, and the kyarabuki pickles are a good palate cleanser.
There is truly nothing not to like about tenmusu. In fact, I think they’re downright charming in their little nori tuxedos… but maybe that’s just me.