I love my local store. This week they have a special on Takase, which is a shell fish that lives out on the reef. I see a lot of them when diving, snorkeling, drowning.
Anyway for a 1000 yen you get a bag of big Takase. You can also get spam, washing powder, octopus, potatoes, rice and stuff.
http://yfn.fc2web.com/yfntakase.html
I slice up the Takase and soak them with onions in soy sauce and mirin.
I cook up a mess of rice.