Following the start of World War II, on 7 March 1942 Ōdachi was appointed civilian mayor of Shōnan (Singapore) under Japanese occupation.

During this period, he was critical of the heavy-handed military administration by the Imperial Japanese Army and its actions against the Chinese population, as well as civilian opportunists who sought to make quick profits under the occupation.

In September 1943, he gave the order to destroy all of the animals at Ueno Zoo, an act recounted in the post-war book Faithful Elephants.

After the surrender of Japan, Ōdachi was (along with all other members of the wartime government) purged from public office by orders of the American occupation authorities.

[4] This led to the passage of a number of laws aimed at enforcing political neutrality in textbooks and in placing restrictions on the hiring of non-civil servants as educators in public schools in 1954.