In one of our recent CSA boxes we got this liquid filled bag - it reads "sashimi konnyaku."
Thanks to the very helpful Kat over at Our Adventures in Japan, I learned that konnyaku is made from yams, and is considered a type of diet food. It can be used a number of different ways, but this type (like a blob of very firm jello) is meant to be eaten like regular sashimi.
So we sliced it up and ate it cold dipped in shoyu. Definitely a unique texture. Fish is not something I miss from my omni days, but for vegetarians who do, this might be a good substitute.