Oshinko (also "Takuan") is a Japanese pickled radish. It has a strong flavor, and so can serve as a single filling in a small (hoso) maki roll, or as an addition to other fillings in Foto-maki, or Ura-maki rolls. Since pickled, the Oshinko can be stored for long periods in the fridge, even after opening - so it's a relatively more convenient to handle than most sushi ingredients. Not only for sushi by the way, Oshinko works well in salads and other cold dishes.