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.

Michiko Ohashi (C), wearing a costume decorated with snacks, performs with other members of pop group Pottya at a fan meeting celebrating her birthday in Tokyo, Japan, October 16, 2016. Competition is cutthroat among Japan's thousands of pop idol wannabes, but a unique concept is winning fame for a band of “chubby” girls deploying their cheeky cuteness to combat prejudices against obesity. (Photo by Kim Kyung-Hoon/Reuters)

A woman with Kimono looks at cherry trees in bloom in Shinjuku Gyoen in Tokyo, Japan on Thursday, April 4, 2024. (Photo by Noriko Hayashi for The Washington Post)

A child reacts as a family takes a break next to a cooling mist at the Sensoji temple as Japanese government issued heat stroke alerts in 39 of the country's 47 prefectures in Tokyo, Japan on July 22, 2024. (Photo by Issei Kato/Reuters)

This photo taken on March 10, 2025 shows the former disaster prevention office building in Minamisanriku Town, Miyagi Prefecture, lit up on the eve of the 14th anniversary of the 2011 earthquake and tsunami disaster. (Photo by JIJI Press/AFP Photo)

Cormorant masters and boatmen prepare sea cormorants for the nights “Ukai” on July 2, 2014 in Gifu, Japan. In this traditional fishing art “ukai”, a cormorant master called “usho” manages cormorants to capture ayu or sweetfish. The ushos of River Nagara have been the official staff of the Imperial Household Agency of Japan since 1890. Currently six imperial fishermen of Nagara River conduct special fishing to contribute to the Imperial family eight times a year, on top of daily fishing from mid-May to mid-October. (Photo by Chris McGrath/Getty Images)

Workers clad in a dog and a wild boar costumes, to represent the outgoing year of the dog and incoming year of the wild boar, clean windows on the side of a hotel in Tokyo on December 13, 2018. (Photo by Kazuhiro Nogi/AFP Photo)