I would like you to correct my sentences to more natural and correct English.
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The supermarket is interesting to see many kinds of Japanese seafood, of course it is a shopping place, and it is not sightseeing place. So, you shouldn’t go there with a large group.

In Tokyo, here is still unknown spot for international tourists. I recommend you to go to this place more than the local fish market.
Here you can watch the cooking view of sashimi at the centrally-placed kitchen every day. You can buy reasonable fresh sashimi, tempura, flied food, etc for to go.

When you buy a whole fish, you can ask the chef to filet it for sashimi. Then, you can probably watch the filleting view. It must be fun, if you are interested in their skillful handling of a kitchen knife. Does this sound natural?

I mostly understand what you are trying to say but I'll make some changes to make it sound a little more natural.

"The supermarket is an interesting place to see many kinds of Japanese seafood. Of course it is a shopping center, not a place for sightseeing so you should not go there with a large group.

Even in Tokyo it is still an unknown spot for international tourists. I recommend you go there instead of the local fish market. ("Here you can watch the cooking view of sashimi at the centrally-placed kitchen every day." I had a hard time understanding what you meant here but I will rewrite it as I understood it) At the supermarket there is a centrally placed kitchen where you can watch the chefs prepare food. You can buy reasonably fresh sashimi, tempura, fried food, and more to go.

When you buy a whole fish you can ask the chef to filet it for sashimi. You may even be able to watch them filet it. It would be fun to watch if you are interested in skillful knife work."