Tendenko is an old Japanese saying that boils down to a brutal instruction: in a tsunami, run and save yourself, do not stop for anyone, not even family. This film tests whether that inherited code explains why the fishing village of Minamisanriku lost so many buildings but kept so many of its people alive when the 2011 Tōhoku earthquake sent a wall of water over its seawalls. A dramatized reconstruction opens the film with the scale of the wave, then it settles into interviews with survivors and disaster researchers who walk through what actually happened in the minutes after the ground shook: who ran, who hesitated, who remembered the drills their grandparents drummed into them as children. Local residents describe the training exercises that turned Tendenko from folklore into muscle memory, and the film treats their accounts as evidence in an argument rather than just testimony. It closes on the community still rebuilding, weighing what a centuries-old survival instruction is worth against everything the tsunami still took.