The post-2014 India-Japan relations converge in Northeast India, with the intersection of the Act East Policy (AEP) and the Free and Open Indo-Pacific (FOIP). This partnership is rooted in socio-economic and security engineering. Japan has emerged as a natural partner in the Northeast, deploying Official Development Assistance (ODA) for infrastructural development. While existing literature highlights this convergence, it often provides only a surface-level account that overlooks the internal heterogeneity, socio-political complexities, and developmental disparities of Northeast India. This study addresses that gap by critically examining Japanese ODA investments in the region through the theoretical framework of infrastructuralism, which interprets how material connectivity at the local level interacts with global political underpinnings. It identifies three dimensions of Japan’s infrastructuralism in the Northeast, i.e. infrastructure as soft power, infrastructure as a site of contestation, and infrastructure as a tool for redefining territoriality and sovereignty. The chapter argues that treating the Northeast as a homogenous unit overlooks its internal socio-political complexities, which can constrain the operationalisation of ODA. To bridge this gap, the study proposes paradiplomacy as a framework for integrating sub-state actors into foreign policymaking, thereby deconstructing and reconstructing the Northeast as a partner in India’s eastward orientation. The findings contribute to International Relations scholarship by situating infrastructuralism and paradiplomacy to offer policy insights for sustainable India-Japan engagement.