Following the Great East Japan earthquake, tsunami and nuclear disaster of 11 March 2011, the Japanese government began constructing a series of 440 seawalls along the north-eastern coast of Honshu. Cumulatively measuring 394.2km, they are designed to defend coastal communities against tsunami that frequently strike the region. We present a case study of the new seawall in Tarō, Iwate Prefecture, which had previously constructed massive sea defences in the wake of two tsunami in 1896 and 1933, which were subsequently destroyed in 2011. We ask whether the government has properly imagined the next disaster for the era of climate change and, therefore, whether its rationale for Tarō‘s new seawall is sufficient. We argue that the government has implemented an incremental strengthening of Tarō‘s existing tsunami defence infrastructure. Significantly, this does not anticipate global warming driven sea level rise, which is accelerating, and which requires transformational adaptation. This continues a national pattern of disaster preparedness and response established in the early 20th century, which resulted in the failure to imagine the 2011 tsunami. We conclude by recalling the lessons of France's Maginot Line and invoke the philosophy of Tanaka Shōzō, father of Japan's modern environmental movement, who urged Japanese to adjust to the flow (nagare) of nature, rather than defend against it, lest they are undone by the force of its backflow (gyakuryū).