Akami is a part of bluefin tuna that refers to lean red meat. This is the main part of the fish, so it's more readily available than the other parts, called chūtoro and otoro. It has the least fat out of the whole tuna, which makes it the most affordable.

Akami is typically used atop rice in sashimi or nigiri. In a sushi restaurant, if you order maguro (a broad term for tuna), you will get akami from whichever species of tuna they have on hand. This part of tuna also has the most umami tuna flavor of all other, fattier cuts.

Otoro is a part of bluefin tuna that is the most desirable. It comes from the inside of the belly and it's the fattiest part of the fish. The texture is often described as intensely rich, marbled, and having melt-in-the-mouth properties. Due to these facts, it's traditionally the most expensive part of bluefin tuna.

It's often used in sashimi and nigiri, giving the dish a sweeter flavor. Otoro is the best during winter, once the tuna acquires additional body fat. It should always be consumed fresh as it doesn't last too much when frozen. This part of tuna is rarely found outside of Japan.

Unagi is the Japanese word referring to the freshwater eel, commonly used in Japanese cuisine. It is mainly consumed in the form of fillets, which are always grilled due to the presence of harmful toxins. The fillets are then spread with a sweet and salty sauce made with soy sauce, mirin, and sugar.

Although unagi is consumed in the entire country, there are slight regional differences in the way the eel is cut and prepared. In Kanto region, the cuts are made from the back, and the fillets are grilled and steamed, while in Kansai the eel is cut from the stomach and the fillets are merely grilled. 

Chūtoro is a part of bluefin tuna that refers to medium fatty cuts when served as a part of nigiri or sashimi. The tuna yields otoro (fatty parts from the belly), akami (red meat), and chūtoro, which is a combination of both that's found near the skin on the back and belly.

It's a mix of otoro's sweetness and a deep, slightly bitter flavor of akami. This part of bluefin tuna is usually a bit more on the expensive side, and it's typically served on special occasions or festivities. Specifically, the part of the back near the head is called sekami, the center of the back is senaka, and the part near the tail is called seshimo.

Fugu is the Japanese word for a fish known as pufferfish, blowfish, or globefish. The fish is infamous for its poisonous parts that contain the lethal poison tetrodotoxin, highly concentrated in the liver, ovaries, eyes, and skin. Trained chefs who want to prepare fugu must undergo scrutinized testing and licensing that is done at local government level.

However, some people prefer the light numbing sensation that the fugu toxin produces, so they ask the chefs to serve them small parts of the toxic organs. In Japan, fugu is usually consumed in specialized restaurants that serve a complete meal which typically includes several courses of the fish served in varying ways, such as fugu sashimi, boiled fugu chiri, fugu rice porridge, or deep-fried fugu.