Midsummer Day of the Ox

When I was a child, I used to think that the Japanese ate eel on the last Saturday of July because "doyou" meant Saturday, and Japanese normally ate eel during summer vacation.

In fact, "doyou" is one of the five elements in Wu Xing or Seasons. It is defined as a particular and discontinuous period identifying accurately the change of season. There are four "doyous" in a year. However, we usually just focus on the "doyou" of the summer season.

When we talk about the origin of "Doyou noushi no hi’’, there are several hypotheses in Japan. The most famous version is that of Gennai Hiraga who pioneered the Dutch Academy and created a particular genre of Japanese literature in Edo era.
An eel merchant, who faced serious slump in his business during the hot summer, asked Hiraga to overcome the bad situation. Hiraga told him that eating eel could help consumers vitalize because eel in Japanese is "unagi" which starts in letter U. In that era, people thought the same letter was believed to be auspicious. As a result, the famous Hiraga’s advice made the eel merchant successful in his business. Consequently, other eel merchants made the same promotion and this culture became deeply rooted in Japan ever since.