Before the Sino-Japanese War began in 1937, Wachi encouraged warlords in south China to revolt against the National government of Jiang Jieshi (Chiang Kai-shek) in Nanjing (Nanking). His targets were Li Tsung-jen and Pai Chung-hsi, but his efforts were not successful. After the start of the war, Wachi headed the Ran (Orchid) Organization. He engaged in efforts to negotiate with the Chinese to end the war and tried to communicate with General Ho Yingqin (Ho Ying-chin), the Chinese chief of staff, via a Chinese agent in 1938, but these efforts failed.
Promoted to major general in 1940, Wachi became chief of staff of the Taiwan Army in March 1941 and simultaneously headed its Research Division, supervising the study of land warfare in Southeast Asia and the Pacific. In February 1942, he became chief of staff of the Fourteenth Army, which assaulted Corregidor Island in the Philippines. Afterward, he had charge of the military government in the Philippines. He was promoted to lieutenant general in 1943.
In March 1944, Wachi was appointed vice chief of staff of the Southern Expeditionary Army and was made chief of staff of the Thirty-Fifth Army fighting on Leyte that November. After the war, he was arrested on war crimes charges for his actions in the Philippines and was held in Sugamo Prison, Tokyo. Tried and convicted by the Yokohama Military Tribunal, he was sentenced to six years at hard labor. He was released on parole in 1950. Wachi died in Tokyo on 30 October 1978.
Hartendorp, A. V. H. The Japanese Occupation of the Philippines. 2 vols. Manila: Bookmark, 1967.; Morgan, Louis. The United States Army in World War II: The War in the Pacific—The Fall of the Philippines. Washington, DC: U.S. Government Printing Office, 1953.