Traditionally, most true katana produced in feudal Japan had a single curved edge and square guard. It was the weapon of choice for the samurai of the era, many of whom carried the katana wherever they went. But Japanese swordsmiths made several different katana swords there, including the double-edged katana.
What is a double-edged katana?
Like all double-edged swords, the double-edged katana has sharp blades on both sides, not just one. They are not as common as traditional single-edged katana swords, although several specimens have still been found throughout history.
The process of making a double-edged katana is different from that of a single-edged katana. For example, differential heat treatment is used differently than a single-edged katana sword (which we'll get to later). After the swordsmith has forged the blade, it is usually passed on to others to sharpen both sides of the sword.
The benefits of a double-edged katana
There really isn't much benefit to using a double-edged katana compared to a traditional single-edged katana. With two blades, some samurai may find it more effective for close combat when engaging multiple enemies. However, to be honest, using a double-edged katana has more disadvantages than using a single-edged katana.
Why a single-edged katana sword is preferred ?
So, what makes a single-edged katana better than a double-edged sword? Perhaps the most significant advantage of the single-edged katana is its ability to be forged through different heat treatments. Japanese swordsmiths heat and cool the edge and spine of the blade at different temperatures, resulting in a hard edge and a soft spine. These properties subsequently made the single-edged katana an advanced weapon at the time, as the blade was less prone to breaking, while the spine retained a certain flexibility—a feature not found on the double-edged katana.
Furthermore, all double-edged swords are difficult to maintain, and double-edged knives are no exception. Samurai fighters must maintain both edges, dealing with shards and nicks on both sides of the sword. Instead of just sanding and repairing one edge, they maintain both.
Finally, samurai cannot sheath a double-edged katana like a traditional single-edged katana. For these reasons and others, the single-edged katana was the sword of choice for feudal Japanese samurai. Even today, most martial arts practitioners and sword collectors would agree that the single-edged sword is the most important thing.