Two volumes of autobiography on his years in Germany narrate his varied experiences during this period.
He died of heart failure on 17 April 2017 at a hospital in Suginami, Tokyo, aged 86.
A conservative opinion-leader affiliated to the openly negationist organization Nippon Kaigi,[2] Watanabe was known for his dismissal of the Nanjing Massacre as a historical delusion, attributing the known killings to the standard revenge of regular soldiers in war against guerrilla combatants whom they have captured.
[3] As he later clarified, in his view, the concept of massacre in war should properly be reserved for atrocities against a civilian population, where the numbers roughly exceed the range of 40–50 victims, as opposed to the wholesale killing of irregular insurgents.
[5] In Watanabe's view, the decisive incident leading to Japan's full-scale war on the Chinese mainland, namely the Marco Polo Bridge Incident in 1937, is to be read as an underhand Chinese Communist Party plot against Japan, and the versions of history taught in pre-war Japanese school textbooks are more reliable than those available today to students.