Most L1 (first language) Japanese speakers in Japan seem to think that they are monolingual. While it appears that Japanese people accept monolingual-ness as normative in the nation, there is little situated understanding of what makes up this Japanese monolingual-ness. This study reports on repeated, long, and mostly unstructured interviews with well-educated 'monolingual' male and female native Japanese speakers regarding their general life histories and experiences including the learning and using of languages, Japanese, English, and others. The four participants also reflected on why and in what ways they were 'monolingual'. The participants' narratives distinctively presented the structural characteristics of the rhizome, as described both in botany and philosophy (Deleuze and Guattari. 1987. "A Thousand Plateaus: Capitalism and Schizophrenia." Translated by B. Massumi. University of Minnesota Press), i.e. a non-centralised structure as seen in the roots of ginger plants and in types of fungi. The analysis revealed that the narratives by the four self-claimed monolinguals were dense and rhizomatic descriptions of the learning and using of social languages (Gee. 1996. "Social Linguistics and Literacies: Ideology in Discourses." Falmer Press); namely, variable language resources that are appropriate to people's functioning as competent participants in particular social activities.