First off, the katana is a terrible weapon. Traditionally forged ones are worse, to the point of not really even being functional in combat. Modern replicas are just awkward.
And, I realize, this runs counter to almost everything you’ve ever heard or read about the katana. Here’s why: the katana isn’t a combat weapon, it is one of the three holy symbols of Shinto. This is where people who aren’t familiar with Shinto can get into a lot of trouble. The attributes ascribed to the katana are talking about the mystical ideal of a perfect blade, not the sword itself.
When you hear about how a master forged katana can cut a silk ribbon in the air, or a leaf on the wind, this is about the mystical katana. It’s what the katana represents culturally. It’s valid, and something to keep in mind, but it isn’t objective reality.
The physical weapon was a very fragile piece of substandard steel. For the Japanese, it was the best they could do, with the mineral resources they had. But it was designed to be as efficient with metal as possible, at the expense of a durable blade.
The primary forging technique behind the katana was a cold steel folding technique, where the iron is beaten into a thin sheet, folded over, and beaten back out again. The process is repeated around ten times to create the steel billet for the blade.
As with the katana itself, the forging technique gets venerated as part of what makes the katana “special.” This glazes over the part where it isn’t an advanced forging technique. It popped up in Northern Europe and persisted into the 1200s. It is a good way to strengthen poor quality iron into cold steel, but it the only notable part about the Japanese technique was the number of folds employed.
In combat the katana kinda sucks. There really isn’t any way around it. Even a modern katana is still a substandard, single bladed longsword. The lack of a second edge prevents reverse strikes. The grip is frequently made out of slick, lacquered wood; exactly the kind of thing a character wants to be trying to keep a grip on in prolonged combat; or silk wrappings, which can, and do, slip during prolonged use. Nearly all combat techniques with a katana focus on a single strike kill, which fails to take into account the nature of actual combat, and even dueling.
One of the major problems with the katana is that because the finishing moves with the blade are supposed to be the same as the opening ones, they leave the swordsman open and vulnerable after each strike. This means that the swordsman needs more time to recover to his starting position, time real combat won’t allow for.
Because of the folding structure, a katana can’t parry or block incoming strikes; the blade will chip apart and need to be completely reforged. There’s no true crossguard. The metal sheet that some Katanas possess is a byproduct of the forging technique, and not really a functional guard.
Modern Katanas get around some of this; modern blades can be forged from high quality steel that historical Japanese swordsmiths didn’t have access to. Modern tempering techniques involve using liquid nitrogen to produce some staggeringly hard metal. Even the folding technique has reverted to lower fold counts, resulting in blades that are more durable, and in some cases, can be repaired. All of this makes for a sword that’s, at least metallurgically, more sound.
It doesn’t address the design flaws, the single edge, the slick grip, or the flaws in the traditional techniques, but, none of this really matters to you.
Here’s the thing, you’re not going into combat with one of these things. Your character is. The katana they’re carrying probably isn’t the real sword; it’s the mythical one. Even before you started reading this article, you already knew if your character was going to fight with one or not.
The use of the katana to prove your character is a badass, or peerless warrior is a bit cliché. But, like the katana itself, the weapon is more of a flash card, informing the reader of exactly who and what your character is and what they’re probably there to do. If you want to play with that, get into the grit of how the real weapons splinter apart in battle, or how the character believes they’re something unrealistic; then you’re starting to break out of the cliché.
What I can say is; be aware that the katana exists as two completely separate swords, the physical weapon, and the metaphysical one. And, be aware that the other exists.