This study analyzes the transformation of Japan's cybersecurity strategy in the digital era, particularly following the adoption of the 2022 National Security Strategy (NSS), which introduced the Active Cyber Defense (ACD) concept for the first time. Japan faces increasingly sophisticated and persistent cyber threats from state-sponsored actors linked to China, North Korea, and Russia, threatening its critical infrastructure, defense systems, and economic assets. Employing a qualitative approach through document analysis and comparative policy analysis, this study utilizes securitization theory from the Copenhagen School complemented by the strategic culture framework as its analytical lens. The findings reveal that Japan's cybersecurity transformation constitutes a paradigmatic shift from an exclusively passive-defensive posture to a proactive defense stance. This transformation is driven by an escalating threat environment in the Indo-Pacific, the deepening of Japan and US alliance cooperation in the cyber domain, and the strategic imperatives of the Free and Open Indo-Pacific (FOIP) vision. However, the pace of transformation remains significantly constrained by Japan's pacifist constitutional framework, domestic political hesitancy, and what scholars have termed structural "Americentrism." This study contributes to theoretical debates on the securitization of cyberspace among middle-power states and offers policy-relevant insights for Indo-Pacific cybersecurity governance.
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