Modern geometry teaching in schools in Japan was modeled on the pedagogies of western countries. However, the core ideas of these pedagogies were often radically changed in the process of adaptation, resulting in teaching differing fundamentally from the original models. This paper discusses the radical changes the pedagogy of a German mathematics educator, P. Treutlein (1845-1912), underwent when adopted by a Japanese mathematics teacher, T. Kunimoto (1895-1985), during the modernization of geometry teaching in the 1930s in Japan.