Tsukudani is any food which has been simmered in soy sauce and sugar (or mirin). It is strongly seasoned and well-preserved and is often put in rice balls. There are many kinds of tsukudani such as sea tangle, laver, beef, clam, eel, small fish, etc.
Karashi-mentaiko is Alaska pollack roe which has been soaked in sake and soy sauce and seasoned with cayenne peppers, dried sea tangle (konbu) and sugar. It is very famous in Hakata (Fukuoka Prefecture in Kyūshū, the southernmost main island in Japan). Mentaiko is not only eaten as a steamed rice topping, but also included in rice balls and spaghetti sauce.
Menma is made by soaking fermented dried machiku (bamboo shoots) in water and seasoning it with soy sauce, sugar, sweet sake for seasoning (mirin) or others. Menma is often used in ramen topping.