Linguistic distancing behaviours indicative of linguistic dissociation (Moore, 2023) have been documented in social scientific and literary accounts focusing on the lives of Japanese-English late plurilinguals (LPs; e.g. Harrison, 2011; Kelsky, 2001; McMahill, 2001; Mori, 1997; Takahashi, 2013). Across these cases, diverse Japanese-English LPs report distancing themselves from their first language (L1), Japanese, often linking it to negative affective states. However, the causes of these distancing behaviours remain underexplained. I share the results of a critical realist grounded theory method study into the causes of L1 dissociation among 17 Japanese-English LPs. Data sources included interviews, narrative elicitation "comfort graphs," and language use journals. My theory posits a complex set of psychological and social causal factors, including the onset of additional language acquisition, the experience of significant intersubjective conflict encoded in their L1 Japanese and the distorting effects of linguaculture ideologies rooted in racist Orientalist logics (Befu, 2001). These findings both further our understanding of linguistic dissociation and, because the data indicate that language education is a primary site for the propagation of these misleading linguaculture ideologies, underscores the importance of better and more critical education for language teachers and, by extension, their students.