Young adults wearing a mask, attends a ceremony as they commemorates the Coming of Age Day of young people entering adulthood in Tokyo, Japan, on January 10, 2022. While the COVID-19 epidemic continues to progress in Japan due to the new Omicron variant, the events that have been organized by the various municipalities of Tokyo have followed a strict sanitary protocol, such as temperature control, disinfection of hands, and the wearing of a protective mask. (Photo by David Mareuil/Anadolu Agency via Getty Images)

Two women in traditional kimonos wear face masks to help curb the spread of the coronavirus as they visit the Sensoji temple in Tokyo on Friday, August 7, 2020. (Photo by Hiro Komae/AP Photo)

Japanese women wearing “yukata” casual summer kimono take selfies at Asakusa district in Tokyo, Japan, 13 September 2020. Asakusa is one of Tokyo's most-visited areas and is usually crowded with tourists. In Japan, the numbers of visitors from abroad fell by 99.9 percent from a year earlier in July due to the ban for entries of foreign visitors amid the coronavirus pandemic. (Photo by Franck Robichon/EPA/EFE)

Mei Hoshizuki and AZM compete during the Women's Pro-Wrestling “Stardom” at Korakuen Hall on September 28, 2020 in Tokyo, Japan. (Photo by Etsuo Hara/Getty Images)

A passer-by takes a selfie with an extra newspaper reporting on President-elect Joe Biden's win in the U.S. presidential election, in Tokyo Sunday, November 8, 2020. The headline reads: “Mr. Biden Assured to win”. (Photo by Eugene Hoshiko/AP Photo)

People wearing face masks to help curb the spread of the coronavirus wait to walk across a traffic intersection in Osaka, western Japan, Thursday, November 26, 2020. (Photo by Hiro Komae/AP Photo)

Only after World War II did the secret spill: Ōkunoshima, located in the Inland Sea of Japan between Hiroshima and Shikoku, was the top-secret site for manufacturing chemical warfare. When the factories were closed down, a number of exotic wild rabbits were seen freely roaming the island. They were assumed to have been the test subjects for the chemical weapons, which the military failed to eradicate when the factory was demolished.