The paper aims to show how Japanese theoretical physics groups emerged between the First and Second World Wars. First, it will be argued that by the early 1930s the Japanese physics community had been predominantly inclined towards experimental physics and that several academic, cultural, and social factors had worked for the maintenance of this status quo. Next, how the situation slowly changed during the early 1930s, and how the young theoretical physicists successfully established a bridgehead during the mid-1930s will be (...) analysed. Four different elements are suggested: the dazzling success of quantum mechanics and its spread in the West; the dominance of experimental physics and its effect on the university system; cultural/social influence; and the emergence of the research network. (shrink)