<p>Japan’s civil defence and civil protection architecture have witnessed a profound transformation since the end of the second world war. This article traces this legislative and structural evolution—tracking the shift from outdated wartime ad hoc systems under imperial legislation to an intricate and codified framework anchored within the scope of Japan’s pacifist constitutional norms. The study traces how the legislature enacted new statutes responding to natural disasters in the post-war era to the slow re-incorporation of civil-military coordination following the Awaji-Hanshin earthquake. The study examines how geopolitical challenges and other relevant factors led to the passing of the Civil Protection Act in 2004, which put several contingencies in place—such as responses to armed attacks and incursions. Through these incremental recalibrations, the study finds that these changes have been legislative and structural, rather than operational; further, they have balanced preparedness against natural and man-made threats while ensuring civilian supremacy over the armed forces despite the shifting security environment.</p>