<p>The Japanese archipelago, situated in subduction zones, consists of island arcs formed at the collision areas of four tectonic plates that cover the Earth. The complex movements of these four plates, which control the crustal structure around the archipelago, drive various crustal processes, including mountain building, volcanic/magmatic activity, fault movement, and seismic activity. This makes the island arcs much more unstable compared to continental landmasses. Extensive surveys and research have been conducted in both terrestrial and marine regions around Japan to elucidate the heterogeneous subsurface structures in seismogenic and volcanic zones. These efforts aim to clarify the mechanisms underlying earthquake and volcanic phenomena and to apply this knowledge for disaster prevention in anticipation of potential future threats. The Japanese geo-electromagnetic research community, organized in the 1950s as a pioneering global entity, has consistently and actively pursued investigations into the subsurface heterogeneous structures and phenomena of seismogenic and volcanic zones of varying scales throughout Japan. This paper synthesizes advances in three-dimensional electrical conductivity imaging conducted over the past two decades at the island-arc scale, with particular emphasis on constraining subduction dynamics by characterizing fluid distribution and its influence on seismic and volcanic processes. Consequently, I suggest that a major forthcoming challenge for the Japanese geo-electromagnetic community is the development and broader implementation of controlled-source electromagnetic methods to improve characterization of the upper kilometer of the crust, along with the enhancement and expansion of rock-physical datasets and modeling frameworks to enable more quantitative interpretations.</p>