Most foreigners think national food or traditional food of Japan is sushi. However, sushi is traditional dish but I think it is not so eaten as much as tempura. However, sushi and tempura have a similarity. Both dishes were sold on streets of Edo(former name of Tokyo). There were sushi vendors and tempura vendors. Therefore these two dishes can be said as local specials of Tokyo.
On the other hand, sushi was invented in Japan but the idea of tempura came from Europe, probably from Portugal. Deep fried foods are popular in Japan but the method of deep frying definitely came from Europe.
The idea of tempura should be a fritter. However, fritter mostly uses seafood, but tempura uses a lot of vegetables and mushrooms. Then, it is dipped to a lukewarm sauce consisting soy sauce.
Tempura is usually accompanied with rice and miso soup but Japanese have invented tendon, tempura on rice. The difference between tempura and tendon is not tempura and rice are separated in each plate or bowl, you do not dip tempura of tendon to a lukewarm sauce. Tendon already comes with sweet thicker sauce similar to sauce used for grilled eel.
Thanks to chained tendon restaurants, you can eat tendon cheaper than before. Then, now less people are cooking tempura at home. Almost no one makes nigiri-sushi at home but someday no one will cook tempura at home either. One of the causes of the fire is when cooking tempura at home. You have to use a plenty of oil and heated up to 180 degrees. If someone calls you and you cannot look after the oil, the flame will appear soon......