Una-ju or Unadon
"It’s simply grilled eel over rice in a box. You might see it on some Japanese restaurants' menus, although 99% of the time it’s an eel already flavored from a package that's warmed up on top of the rice.
If you’re in Japan there are Unagi-ya, which are dedicated eel shops. They first fillet an eel, skewer (or steam, depending on the region), dip the skewer in a sauce, and grill to perfection. Some shops have used the same dipping sauce for generations, adding an umami that you cannot create overnight. To master the art of making unagi they say 'skewering three years, filleting five years, grilling lifetime'. If you’re in Japan, I would suggest seeking out one of the old-school shops near the Asakusa or Ginza area. I think it’s great; it really melts in your mouth, and it also has nice charred and smoky flavors. - Tatsu Aikawa, executive chef/owner, Ramen Tatsu-Ya (Austin, TX)