This chapter critiques the dualist assumptions underpinning gender analysis in IR, particularly the persistent division between masculine and feminine categories that structures both universalist and particularist gender epistemics. It shows that, despite their differences, mainstream and critical approaches remain grounded in a shared commitment to separability, reproducing binary distinctions that limit the analysis of gendered political life. In response, the chapter develops Concomitance as a nondualist methodological model that reconceptualises gender as a simultaneous and interpenetrating field of masculine and feminine energies. Drawing on Daoist nondualism as expressed through yin–yang and Advaita-inspired notions of ardhanarishvara, it advances a framework that foregrounds simultaneity, changeability, and reversibility. This framework is operationalised through the concomitance tracking procedure (CTP), which traces the ongoing interplay of these energies across political contexts. Applied to gendered nationalism and diplomacy, the chapter shows how Concomitance reconfigures entrenched binaries and enables a post-binary understanding of gendered dynamics in contemporary international politics.