Yuasa was born in Saitama prefecture and grew up in Tokyo, Kyobashi district. He decided to follow his father's example and, after graduating from Jikei University's School of Medicine in March 1941, became a doctor. He had originally hoped to become a rural practitioner traveling to remote villages that had no doctor and helping to treat underprivileged patients. However, along with the vast majority of able-bodiedyoung men in Japan, he was soon drafted into the Imperial Army.
War experiences
Within six weeks into the beginning of his service in China, Yuasa was conducting vivisections of prisoners. The Japanese army believed in the importance of performing operations on live prisoners as a way of learning how to better care for Japanese casualties. Yuasa's first vivisection was in March 1942 in the army hospital in Changzhi in Shanxi Province. Two Chinese prisoners—a younger man and an older man—were handcuffed to operating tables while 20 other doctors and nurses observed. First, an appendectomy was performed on one of the conscious patients, after which the doctorsutured the wound, and then a tracheotomy. Impelled by interest, Yuasa went on to perform an amputation of the right arm of one of the prisoners. Yuasa admits being afraid during the course of this vivisection, but by his third trial, he admits to being a willing participant. He recalls an additional incident when he operated on a Chinese prisoner who had been deliberately shot so he could be operated on as practice for a "real situation". He was under orders not to use anesthesia. Yuasa was later put in charge of a clinic where he repeatedly dissected Communists, delivered to him by the police upon request, all for practice purposes. Yuasa has said that in all he participated in six such vivisections. Aside from this practice of vivisection, Yuasa also cultivated typhoid germs and supplied these to the Japanese armed forces for biological warfare against Chinese Communists. After the war ended, Yuasa became a prisoner of war in China. He was compelled by his captors to record on paper all of the atrocities he had committed as a doctor in China. It was not until he began to write down in detail his past actions, that he began to realize the magnitude of what he had committed. In 1956, he was released and allowed to return to Japan.
Post-war activism
Hoping to act as a reminder to Japan that these atrocities must never be repeated, Yuasa was one of a handful of doctors who eventually confessed their crimes to the Japanese public and the world. Subsequent to his return to Japan in the 1950s he publicly detailed the army's atrocities. He received death threats from Japanese nationalists, and was advised by former colleagues at the Luan army hospital to "go easy" on his revelations. Until his death, Yuasa continued touring Japan to tell audiences of his wartime experiences.
