Japan recorded its first official "kokushobi", or "cruelly hot day", on Tuesday as temperatures in the central cities of Gujo, Tajimi and Toyota exceeded 40°C, according to the Japan Meteorological Agency. The new term, introduced in April to describe days when the mercury reaches 40°C or higher, was applied as a persistent high-pressure system kept temperatures above that threshold for a second consecutive day, the national broadcaster NHK reported. Heatstroke alerts were issued across 41 of Japan's 47 prefectures, and the Tokyo Fire Department said 287 people aged three to 103 were taken to hospital in the capital on Tuesday with suspected heatstroke, the highest single-day figure this year.

The extreme heat has prompted the Tokyo Metropolitan Government to expand its "Tokyo Cool Biz" campaign, encouraging office workers to wear shorts, T-shirts and trainers instead of suits and ties. Noboru Watanabe, an environmental official for the metropolitan government, told the BBC: "We want to give people more options in the severe heat, not tell them what to wear. There should be no issue as long as the work attire is not offensive to anyone." The initiative, introduced by Governor Yuriko Koike in April, has drawn mixed reactions. A June survey by Gorilla Clinic found 53.5 per cent of respondents opposed wearing shorts to work, while 46.5 per cent supported the idea. Among those opposed, concerns over body shape and body hair were the main reasons for both genders, the clinic said.

The policy has also sparked debate over gender fairness. Some women have described the experience of seeing male colleagues' bare legs as "sunehara", or "leg hair harassment", a term coined online to express discomfort. Women have also noted that they are still expected to wear tights when showing their legs at work, according to reports by the BBC and other outlets. Akifumi Funatsu, director of Gorilla Clinic, told the BBC that more men were seeking laser hair removal not just for cosmetic reasons but as a matter of "social etiquette when wearing shorts".

The heatwave has already caused fatalities. An 85-year-old farmer was found dead inside a greenhouse in Tochigi prefecture on Tuesday, and three people over 70 died on the first day of the extreme heat, Kyodo News reported. According to the Fire and Disaster Management Agency, 4,580 people were admitted to hospital for heatstroke in the week from 6 to 12 July, including seven deaths. Last year, more than 100,000 people were hospitalised with heatstroke between May and September, and heatstroke deaths topped 2,000 for the first time in 2024, the agency said. The summer of 2025 was 2.4°C above the average of the previous three decades, and Japan's all-time high of 41.8°C was recorded in August 2025 at Isesaki, Gunma prefecture.

The Cool Biz campaign was first launched by Koike in 2005 when she served as environment minister, encouraging workers to abandon jackets and ties to reduce reliance on air conditioning. After the 2011 Tohoku earthquake and tsunami, the government expanded it into "Super Cool Biz" with broader energy-saving measures. The Japan Meteorological Agency has warned that the current heat is expected to persist into next week, and authorities continue to urge residents to use air conditioning, stay hydrated and avoid prolonged outdoor activity.