What
is Unagi? 
Unagi (eel) has been consumed in Japan since the 17th century. It used to be expensive food, but Unagi can be reasonably purchased nowadays. Unagi is rich in protein, calcium, vitamin A and E, and it's believed to give people stamina. So, unagi dishes are eaten the most during the hottest time of the year.
A common unagi dish is unagi no kaba-yaki (grilled eel). Prepared unagi meat (the main bone is removed) is skewered and grilled with sweet basting sauce. It's similar to teri-yaki. Most people in Japan buy unagi no kabayaki at stores instead of making it themselves. Before eating kabayaki, you only have to reheat it with kabayaki sauce. To make your own kabayaki sauce, mix 1/2 cup of soysauce, 1/2 of mirin, and 1/4 cup of sugar in a pan and simmer it until thicken.
The way of cooking kabayaki is slightly different between eastern Japan and western Japan. In eastern Japan, unagi is steamed after it is grilled, then it's grilled again. In the western part of Japan, unagi isn't steamed. So, unagi no kabayaki in eastern Japan tends to be softer than that of western Japan. Grilled unagi without basting sauce is called shira-yaki since it's white. (shira indicates the color of white in Japanese.)
When unagi is grilled over charcoals, the fat from unagi drips and burns, causing smoke. The smoke adds a great flavor to unagi. The smell coming from an unagi restaurant tends to invite many customers.
Commonly, unagi no kabayaki is served over plain rice as a main dish. It's called either una-juu or una-don. Clear soup (suimono) made from unagi liver is called kimo-sui and is served on the side. I'll introduce two simple dishes you can make with unagi no kabayaki.
Unagi no kabayaki
Ingredients:
1 skewered unagi no kabayaki (cold)
2 cucumber
3 tbsp Japanese rice wine vinegar / 1 tbsp sugar / 1 tbsp soy sauce
Cut unagi no kabayaki into bite-sized pieces.
Thinly slice cucumbers into rounds.
Put cucumber slices and unagi pieces on a plate.
Mix soy sauce, sugar, and vinegar together and pour over the cucumber and unagi.