Japan’s Hottest Season and the Day of the Ox
Life in Japan – Issue 036
On July 23, Japan entered 大暑（Taisho / Greater Heat）, one of the 二十四節気（nijūshi sekki / twenty-four solar terms）.
The twenty-four solar terms divide the year into 24 periods based on the movement of the sun, with each period given a name that reflects the season. True to its name, Taisho marks one of the hottest times of the year.
This year in Japan, those words no longer feel like a seasonal expression. They describe the reality right in front of us.
In Japan, hot days are given different names according to the day’s highest temperature. A day that reaches 25°C（77°F）or above is called 夏日（natsubi）. At 30°C（86°F）or above, it becomes 真夏日（manatsubi）, and at 35°C（95°F）or above, it is 猛暑日（mōshobi）. This year, the Japan Meteorological Agency officially decided that a day reaching 40°C（104°F）or above would be called 酷暑日（kokushobi）.
In recent years, temperatures above 40°C have been recorded almost every summer. Japan needed a new term to describe a level of heat beyond mōshobi.
On July 23, the day Taisho began, the temperature reached 41.1°C（106.0°F）in Sakuma, Hamamatsu City, Shizuoka Prefecture. This tied for the sixth-highest temperature ever recorded in Japan. On the same day, Toyota City in Aichi Prefecture and Mino City in Gifu Prefecture both recorded 40.8°C（105.4°F）. The following day, the temperature also reached 40.8°C（105.4°F）in Kuwana City, Mie Prefecture.
In a country where a day above 25°C（77°F）is already called natsubi, temperatures more than 15°C（27°F）above that threshold are now being recorded. Describing this as “life-threatening heat” is no exaggeration.
During the week from July 13 to 19, 10,857 people across Japan were taken to hospital by ambulance for heatstroke. That figure covers only the period through July 19. Since then, temperatures above 40°C（104°F）have been recorded in one place after another, and the intense heat has continued. I think the number of people transported by ambulance from July 20 onward may be even higher when the next figures are released.
I am currently in Nagano Prefecture for work.
Nagano has many high-altitude areas, some of which are well known as summer retreats. Even so, the prefecture is experiencing record-breaking heat this year. On July 23, the temperature reached 39.5°C（103.1°F）in Minamishinano, in southern Nagano. This tied the highest temperature ever recorded in the prefecture.
In Suwa, where I am staying, the temperature reached 35.4°C（95.7°F）on July 22, making it a mōshobi. I had thought Nagano would be a little cooler, but simply moving around outside drained my energy. After continuing with my reporting and other work, I found myself completely worn down by the heat.
In Japan, the physical fatigue, sluggishness, and loss of appetite caused by prolonged heat are known as 夏ばて（natsubate / summer fatigue）. When people begin to feel natsubate, many say, “I need to build up my stamina.”
Here, stamina does not refer only to physical performance. It is an everyday way of talking about eating something nutritious to regain the energy lost to the heat.
During the Japanese summer, cold noodles and shaved ice are easy to eat even in hot weather. At the same time, there is also the idea that eating foods that seem restorative, such as meat, garlic, and 鰻（unagi / eel）, will help us make it through the summer.
In a previous article, I wrote about unagi while introducing some of Japan’s freshwater fish. Unagi has been eaten in Japan for centuries, but today it is expensive and no longer something people can enjoy casually. Eating it at a restaurant that specializes in unagi feels a little more special than an ordinary meal.
So even though I wanted to eat unagi, I felt that I needed a few reasons.
土用の丑の日（Doyō no Ushi no Hi / Day of the Ox during Doyō）was approaching. Every day was hot, and I was already suffering from natsubate. The area around Lake Suwa, where I am now, is also known for unagi. And I was away on a business trip, working every day.
With that many reasons lined up, I began to feel that I could allow myself to eat it.
I ate unagi at a restaurant near Lake Suwa. Doyō no Ushi no Hi was still a few days away, but I decided that I was eating it to help myself withstand the heat. I borrowed some of the unagi’s strength a little early.
Wild unagi were once caught in Lake Suwa. As a result, there are still many restaurants serving unagi around the lake. Okaya City, on the western side of Lake Suwa, is especially well known as うなぎのまち（unagi no machi / the town of eel）. Unagi has long been enjoyed by the people of Okaya and has become part of the area’s distinctive food culture.
Eating unagi near Lake Suwa gave me another reason beyond Doyō no Ushi no Hi: this was the right place to eat it.
So what exactly is Doyō no Ushi no Hi, the day that Japanese people talk about every summer?
土用（Doyō）is pronounced the same as 土曜（doyō）, the Japanese word for Saturday, but the two words are written differently and have entirely different meanings. Doyō does not refer to a single day either.
Doyō is a period of roughly 18 days just before the seasons change. The Japanese calendar includes 立春（Risshun / Beginning of Spring）, 立夏（Rikka / Beginning of Summer）, 立秋（Risshū / Beginning of Autumn）, and 立冬（Rittō / Beginning of Winter）. Each marks the beginning of a new season. Because Doyō comes before each of these seasonal turning points, there are actually four Doyō periods every year.
This idea comes from 五行思想（gogyō shisō / the theory of the Five Elements）, which was introduced to Japan from ancient China. This system groups aspects of the natural and human worlds into five elements: wood, fire, earth, metal, and water. Wood was assigned to spring, fire to summer, metal to autumn, and water to winter. Earth was assigned to the periods between the seasons.
In Japan today, Doyō usually refers to the summer period before Risshū. In 2026, the summer Doyō began on July 20 and continues until August 6, the day before Risshū.
丑（Ushi / Ox）is one of the twelve signs of the zodiac, following 子（Ne / Rat）and preceding 寅（Tora / Tiger）. The zodiac is also known overseas as a way of identifying a person’s birth year. In the past, however, Japan assigned a zodiac sign not only to each year but also to each day.
Imagine assigning the twelve zodiac signs to the calendar one day at a time. The first day is 子の日（Ne no Hi / Day of the Rat）, the next is 丑の日（Ushi no Hi / Day of the Ox）, and the following day is 寅の日（Tora no Hi / Day of the Tiger）. After reaching the twelfth sign, the Day of the Boar, the cycle begins again with the Day of the Rat. This means that Ushi no Hi returns every 12 days.
Because Doyō lasts for about 18 days, it contains one Ushi no Hi, or sometimes two depending on the year. An Ushi no Hi that falls within the Doyō period is known as Doyō no Ushi no Hi. In the summer of 2026, it occurs only once, on July 26.
Why, then, do people eat unagi on Ushi no Hi?
The connection between unagi and summer has a long history. Unagi even appears in 『万葉集』（Man’yōshū）, Japan’s oldest poetry collection, compiled in the eighth century. The poet 大伴家持（Ōtomo no Yakamochi）wrote a poem telling a man named 石麻呂（Ishimaro）, who had grown thin during the summer, to catch and eat an eel because it was said to be good for summer weight loss.
This was not a serious record of a health remedy, but a humorous poem teasing a thin friend. Even so, it shows that unagi was already associated with the hot season in Japan more than a thousand years ago.
鰻の蒲焼き（unagi kabayaki / grilled eel glazed with sauce）contains protein and fat, as well as vitamins A, D, and several B vitamins. Eating unagi once will not protect anyone from the heat, but it is certainly a nutrient-rich food.
The best-known explanation for how the custom of eating unagi on Doyō no Ushi no Hi became widespread is a story about 平賀源内（Hiraga Gennai）, an Edo-period scholar and inventor.
According to the story, an unagi restaurant owner was struggling because eel did not sell well during the hot season. He asked Gennai for advice, and Gennai suggested putting up a sign outside the restaurant that read, “Today is Doyō no Ushi no Hi.” At the time, there was a belief that eating foods whose names began with the sound “u” on Ushi no Hi would help people avoid summer fatigue. The Japanese word for eel is unagi, so it fit the belief perfectly.
The restaurant prospered after putting up the sign, and other unagi restaurants began using the same idea. The practice is said to have spread throughout Edo and eventually became the custom of eating unagi on Doyō no Ushi no Hi.
No definitive historical record remains to prove that this story was the origin of the custom. There are several theories about the connection between Doyō no Ushi no Hi and unagi. Even so, the story of Hiraga Gennai remains the best-known explanation today. Its appeal may also come from how easy it is to understand: an advertisement from the Edo period gave rise to a seasonal custom that has lasted for generations.
In Japan today, not everyone eats unagi only after learning about Doyō or the theory of the Five Elements. There are also few occasions in everyday life when people think about the zodiac sign assigned to each day.
Yet as the summer Doyō approaches, signs announcing Doyō no Ushi no Hi appear at unagi restaurants and supermarkets. Unagi is featured on television and in the news, and when people realize that the day is approaching, they decide to eat it simply because “it is Doyō no Ushi no Hi.”
Some people know the history well. Others enjoy it as a seasonal custom without knowing the details. Japanese has a word for this: あやかる（ayakaru）. It describes the feeling of connecting yourself with an auspicious person, object, or special occasion in the hope of sharing in its good fortune or power.
Even expensive unagi becomes a little easier to justify when the reason is, “Today is Doyō no Ushi no Hi.” A date on the calendar gives people the final push to choose a meal they might otherwise hesitate to buy.
The intense heat will continue for a while. Please take care of yourselves, and once in a while, perhaps give yourself a little indulgence. Find something to ayakaru, and enjoy something a little more expensive than usual.
And if you have the opportunity to visit Japan, please try unagi. Even if it is not Doyō no Ushi no Hi, I am sure you will find a reason to eat it.
—Written by Sumire
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This is such a rich piece. The temperature hierarchy — natsubi, manatsubi, moshobi, kokushobi — maps beautifully onto the old almanac's layered system. What struck me is that 大暑 (Taisho) and 土用 (doyō) overlap but serve completely different functions: Taisho marks the solar position, while doyō marks the earth element's instability between seasons. The sealed calendar reads both simultaneously and gives different instructions for each. We cover the doyō-to-Risshū transition at Japan Deep Ritual — specifically how the almanac treats the last days of earth-season as a threshold, not just a weather event. Would love to hear how you two experience the shift from 土用 into 立秋 living in Japan.