It’s often (but not always) available at supermarkets, but it’s not commonly eaten. Hopefully the tradition will die off with the older generations.

It’s not the most popular but it is eaten. My local supermarket sells it.

I think that it’s been a thing for a while. Japan’s an island nation, and harvesting sea life has been important. Probably some people who want it just for tradition.

kagis

https://en.wikipedia.org/wiki/History_of_whaling

The oldest written mention of whaling in Japanese records is from Kojiki, the oldest Japanese historical book, which was written in the 7th century CE. This book describes whale meat being eaten by Emperor Jimmu. In Man’yōshū, an anthology of poems from the 8th century CE, the word “Whaling” (いさなとり) was frequently used in depicting the ocean or beaches.

One of the first records of whaling using harpoons is from the 1570s at Morosaki, a bay attached to Ise Bay. This method of whaling spread to Kii (before 1606), Shikoku (1624), northern Kyushu (1630s), and Nagato (around 1672).

Kakuemon Wada, later known as Kakuemon Taiji, was said to have invented net whaling sometime between 1675 and 1677. This method soon spread to Shikoku (1681) and northern Kyushu (1684)

Using the techniques developed by Taiji, the Japanese mainly hunted four species of whale: the North Pacific right, the humpback, the fin, and the gray whale. They also caught the occasional blue, sperm, or sei/Bryde’s whale .

In 1853, the US naval officer Matthew Perry forced Japan to open up to foreign trade. One purpose of his mission was to gain access to ports for the American whaling fleet in the north-west Pacific Ocean. Japan’s traditional whaling was eventually replaced in the late 19th century and early 20th century with modern methods.

https://education.nationalgeographic.org/resource/big-fish-history-whaling/

People have been whaling for thousands of years. Norwegians were among the first to hunt whales, as early as 4,000 years ago. The Japanese may have been doing so even earlier.