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.

Carrying a portable shrine on their shoulders, participants all clad in traditional happi coats, parade through precincts of the Kanda Myojin shrine during the annual summer festival in Tokyo, Saturday, May 9, 2015. (Photo by Eugene Hoshiko/AP Photo)

Women in yukatas, or casual summer kimonos, take their selfie in front of paper lanterns during the annual Mitama Festival at the Yasukuni Shrine, where more than 2.4 million war dead are enshrined, in Tokyo, Japan July 13, 2017. (Photo by Kim Kyung-Hoon/Reuters)

A performer wearing a lion mask performs the Ise Daikagura lion dance at the remote village of Yamanawa on February 08, 2021 in Ryuo, Japan. Ise Daikagura is a group of traditional Lion Dance performers who pray in front of farmers houses and businesses for good grain harvests and disease-free lives. (Photo by Buddhika Weerasinghe/Getty Images)

Women in Kimono holding an umbrella walk on a street at Ginza shopping district in Tokyo, Japan, March 31, 2016. (Photo by Yuya Shino/Reuters)

A deer walks across a pedestrian crossing in Nara, Japan, Thursday, March 19, 2020. More than 1,000 deer roam free in the ancient capital city of Japan. Despite the town's tourism decline, these wild animals are doing just fine without treats from tourists, according to a deer protection group. (Photo by Jae C. Hong/AP Photo)

People wrapped in blankets sit on the road as they are evacuated from a hotel after an earthquake in Kumamoto, southern Japan, in this photo taken by Kyodo April 14, 2016. A powerful earthquake with a magnitude of 6.5 knocked over buildings in southern Japan on Thursday evening, and police said people may be trapped underneath. (Photo by Reuters/Kyodo News)

Participants with traditional Japanese tattoos (Irezumi), related to the Yakuza, walk through the Asakusa district during the annual Sanja Matsuri festival in Tokyo on May 20, 2018. Sanja Matsuri festival is a celebration for the three founders of Sensoji Temple in the Asakusa neighbourhood with nearly two million people visiting during the three-day event. (Photo by Behrouz Mehri/AFP Photo)