Focusing on Japan, this paper explores whether powers and competences in the political system are likely to be recalibrated in favour of the executive when the environment is perceived as increasingly threatening. It shows that the executive has been significantly strengthened during the past two decades of political reforms, though a closer look reveals that only the most recent efforts are motivated by security concerns. Case studies on military deployments and arms exports do not expose any clear trend towards curbing parliament's formal control powers, but they indicate two related mechanisms that affect executive–legislative relations. Firstly, the executive has sought to ensure faster decision-making in security policy, which may limit the Diet's ability to scrutinise policies in depth. Secondly, the level of contestation over security policy issues has been decreasing, especially given the securitisation of North Korea and China. This provides the executive with more leeway in devising policies.