Just to point out, many of these Japanese citruses are complex hybrids (but not intentional hybrids) between Kunenbo (a type of tangor-like fruit, basically almost mandarin with some pomelo in its ancestry, probably came from China), Kishu (very small but great quality mandarin, also probably came from China), Tachibana (a mandarin sub-species, only citrus native to the Japanese islands, not that good eating equality), and to a lesser extent Yuzu (also came from China, the Japanese named it after the Chinese word for pomelo, since it was sour).
Shikuwasa may have come from Taiwan or the Ryukyu islands, and appears to share close common ancestry with Tachibana but not directly descended from it. Shikuwasa also appears to have some distant ancestry from Yuzu.
Keraji originated from Shikuwasa that apparently got backcrossed three times over the years with Kunenbo. It's also very hardy, down to 8b, probably could survive 8a in certain conditions. Supposedly great flavor and easy to peel, but very small and seedy.
Kabosu is apparently a cross between Yuzu and Kunenbo.
I'd like to point out that many of these unique citruses are very regional and traditional, and their use in modern Japan had mostly died out, especially due to large-scale commodity imports of citrus from the United States, since the high cost of living makes commodity agriculture prohibitively expensive in Japan. Native-grown Japanese citrus is considered a more expensive delicacy in typical Japanese supermarkets. Probably much of the Japanese public has no idea what these citrus even are.
Yuzu though has seen a popular resurgence in Japan, with Yuzu extract being sold in markets, and Yuzu flavored alcohol commonly being available in establishments. Satsuma has been the most popular mandarin in Japan for a couple hundred years, the word mikan has almost become synonymous with the Satsuma variety in modern Japan, and most people will buy them in the supermarkets when in season. Sudachi and Kabosu are basically known as the two less common "forms" of Yuzu by the ordinary public in Japan, they are not as often seen but can usually be found for sale in the large fish markets.
Yuzu has its own unique flavor and fragrance. If you've never tasted it before, it really is unique from other citrus types. It's almost like a very fragrant - almost floral - sour orange (marmalade orange), but with a pungently deep spiciness, but also like lemon as well, mixed with perhaps some Satsuma mandarin and regular mandarin, and for the most discerning, perhaps the tiniest sweet top note of artificial grapefruit and guava.