In a traditional katana, the sharp part is the cutting edge, which is the front edge of the blade that extends from the tip to the base of the sword. The cutting edge is typically single-edged, meaning it has a beveled edge on one side, while the other side, known as the back or spine, is unsharpened and usually flat or slightly rounded.

The cutting edge of a katana is honed to a very sharp edge using meticulous craftsmanship and techniques. It is the portion of the blade that is designed to make contact with the target during a strike, slash, or cut. The sharpness of the cutting edge allows the katana to efficiently and effectively slice through objects or penetrate targets.

It's important to exercise caution and handle a katana with care, as the sharp cutting edge can cause serious injury if mishandled or used improperly. Respecting the weapon and adhering to proper sword handling techniques are crucial for maintaining safety and preventing accidents.