The curve of a katana is the first thing the eye loves and the last thing most buyers understand. That curve is the sori (反り, pronounced “soh-ree”) — the gentle arc of the blade. Here is the part that surprises people: on a true Japanese sword, the smith does not bend that curve in. The fire does it.
What Sori Really Is
Sori is the depth of the blade’s curvature, measured as the gap between the back of the steel and a straight line drawn from base to tip. A katana starts life nearly straight on the anvil. When the clay-coated blade is plunged into the quench, the hard edge, or ha and the soft spine, or mune cool at different rates and pull against each other — and the blade springs into its arc. The curve is a fingerprint of the quench itself.
How the Curve Is Read
Not all curves sit in the same place. Koshi-zori leans the deepest point toward the base near the tang, or nakago; tori-zori centers it evenly; saki-zori pushes it toward the point, or kissaki. Where the curve lives changes the sword’s character — a deeper, base-heavy sori reads as classical and elegant, a shallower one as fast and modern. See how it relates to the rest of the steel on our katana anatomy guide.
Why Sori Matters When You Buy
Curve is not decoration — it is cutting physics. A curved edge slices as it passes through a target instead of chopping, drawing the steel across the cut like a long, smooth pull. The right sori for you depends on how you intend to use the sword: more curve for elegant draw-cuts, less for thrust-leaning work. A blade whose sori came from a real differential quench will also carry a hamon temper line, so the two go hand in hand. Browse our katana collection, study how the curve is forged, and if you are new, let our guide to choosing a katana point you to the right arc.