It is believed that sushi has its roots in Southeast Asia where fish and meat were salted, then fermented for long periods of time. Records of similar methods of fermented fish are first seen in Chinese scriptures in the 2nd century. It also seemed that it wasn’t the most popular dish at the time. This type of sushi is documented in Japan in the 7th century. It was later in the Heian period or during the 10th century when uncooked rice was stuffed inside the fish after they were gutted, and cleaned with sake or Japanese rice wine, before they were fermented. A fresh water fish such as carp was often used for this type of sushi, and was called the nare sushi (ripe sushi). The rice aided in the fermentation process and made it quicker to prepare than the original sushi. The rice was discarded after the fermentation was complete (a period of 2 to 3 months depending on the season) and only the fish was consumed.
During the Muromachi Period, or 15th century, the nare sushi began to divide into two types, the hon nare (true ripe) and nama nare (raw ripe, or pre-ripe). The hon nare is the original version of the sushi which began its roots in the 10th century. The nama nare is the same type of sushi, but it is consumed prematurely. This way the rice stuffed inside the fish to aid the fermentation process became somewhat edible. The nama nare sushi is distinct from the hon nare in a way that it has a more pleasant sour taste. Eventually the nama nare became more popular for its quicker preparation and it’s extra side dish, the fermented rice which had a mild tangy flavor to it.
About a hundred years later, vinegar was beginning to be added to cut the preparation time even further. This way, only minimal time was required for fermentation, since vinegar was added later to artificially create the tangy taste. This was not done just to cut time and cost for hon nare or nare sushi production. It was actually more favorable to people, since nare sushi in general has a very pungent smell, and was not widely appreciated by many, even though it was (and still is) considered a delicacy. From here on, less and less fermentation was required to create nare sushi, and eventually a new type of sushi using only fresh vinegar and cooked rice began to evolve. This began a trend of new types of sushi being evolved in local areas, such as the Osaka style sushi, Oshi sushi, chirashi sushi and nuku sushi just to mention a few. All of these are still popular in Japan.