Korehira Watanabe is one of Japan's last traditional swordsmiths, and this film follows him through the forge as he tries to recreate the Koto blades, swords made before the 1500s using techniques later generations lost. Forty years into his career, Watanabe folds and hammers steel, works the clay coating that controls the blade's temper line, and quenches finished swords in water, explaining at each stage why the old masters' results have proven so hard to reproduce. The camera stays close on the physical work: glowing metal under the hammer, the charcoal fire, the fine grinding and polishing that takes a blade from rough bar to mirror finish. Interviews with Watanabe give the film its throughline, his frustration and persistence as decades of experiments edge him closer to matching a standard set centuries ago. There is little else in the way of narration or history beyond what he supplies himself, which keeps the focus tight on one craftsman's attempt to solve a problem that has outlasted several generations of swordsmiths before him.