
Japan
Mazezushi
Warm sushi rice tossed with salted salmon, shiso, takuan and scrambled egg
Daikon radish pickled in salt and rice bran or a sweet-salty brine, usually bright yellow, crunchy, sweetish and salty.
Takuan is pickled daikon, a long, mild white radish. Traditionally it is dried and then fermented in salt and rice bran; today it is often pickled more quickly in a sweet-salty brine and coloured yellow with turmeric or other colourings. It is firm and crunchy, tastes sweetish, salty and slightly sour, and has a distinct fermented smell, especially when made the traditional way. That crunch and sweetness are what make it valuable as a side to rice and as a filling for sushi rolls. You can find it in Asian grocery stores, whole or in vacuum-packed strips in the chilled section or among preserved goods, and by mail order.
Korean danmuji is essentially the same thing, a yellow sweet pickled radish, and can be swapped in directly. Daikon or white radish quick-pickled at home in vinegar, sugar, salt and a pinch of turmeric matches the crunch, sweetness and colour, but not the deeper fermented flavour of rice-bran pickling.

Japan
Warm sushi rice tossed with salted salmon, shiso, takuan and scrambled egg