Cai was fired from his job as a teacher at the Tainan Number 2 Common School for his involvement with the Assimilation Society. Lacking local prospects, in 1915 Cai enrolled at Tokyo Higher Normal School, the most prestigious teacher training college in the empire. Lin Hsien-t’ang, the founder of the Assimilation Society, paid his tuition. In 1920, he became the first “special student” (tokubetsu gakusei) from Taiwan to graduate from the school.
Cai’s days at Tokyo Higher Normal School were formative ones. In Tokyo, Cai stayed at the “Takasago Dormitory” (Takasago ryō). There, he met others intent on upending Taiwan’s subordination to the inner territory (Komagome 2015, 33; Heylen 2007, 242). Cai stayed in Tokyo until 1922. During this time, he worked with other Taiwanese students in the metropole to found the magazine Taiwan seinen (Taiwan youth) and the Shinminkai (New People’s Society). Through this work, Cai developed his “dialogical approach” (taiwa rosen) to political activism (Oguma 2017, 297 [1998, 329]). Opening the fifth issue of Taiwan seinen, Cai described the necessity of dialogue to achieving the organization’s political ends: “The majority of people of the motherland are longing to talk with us, and it is time to rise to action and bring what we truly think to the attention of all people of the nation (zen kokumin); and, in cooperation with all people of the nation, carry out a fundamental reshaping within our island” (Oguma 1998, 329, quoting Cai, “Kantō no ji,” Taiwan seinen 1, no. 5 (1920): 1); translation modified from Oguma 2017, 297).