The katana is the traditional Japanese sword. It has a long handle, and is designed to be used either one or two handed. It has a slight curve. Japanese culture considers it to be one of the most beautiful things in the world.
A huge amount has been written about the katana. Much of this has been written by people determined to prove to the world that the katana was the most awesomely fabulous weapon ever, and that anyone with a katana would easily slaughter anyone with any other weapon. This is of course nonsense. The skill of the fighters is a major factor in any fight. When Portuguese swordsmen fought Japanese katana-wielding samurai, the result was a draw. The katana man would kill his foe with a single blow, if he could get the single blow to land, but the rapier man would often win by inflicting a dozen stabbing thrusts, between deflecting the blows from the samurai.
Much is written about the way in which katanas were made, stressing how the metal of the blade was folded over and over by experts, and welded into a strong blade made up of hundreds of layers. It is true that the best katanas were well made, but it is also true that many katanas were rubbish. You cannot expect every one of countless thousands of swords, over many centuries, to have been made by the finest craftsmen, using the finest materials. It is also true that other weapon-smiths around the world used pattern welding. The Saxons and Vikings had many tricks to improve their swords, including making square section rods, then twisting these in to spiral vortexes and then hammering them back square; plaiting three or five of these together; welding on a different hardness of metal for the edge of the blade. By comparison, the Japanese method starts to look primitive.
Much has been written about the tiny details of the katana, such as the particular design of the hand guard. In some periods and places these are oval, in others octagonal, and so forth. An expert can look at a katana and sometimes tell when and where it was made. I am not this sort of expert.
Once, I was very lucky to be visited by a collector of katanas, and he brought his swords. He lined them up, leaning them against the wall in their scabbards, in chronological order. The newest of them dated to the Second World War, and the oldest to the twelfth century. The first thing that struck me was how amazingly similar they all were. They were all about the same length, give or take a couple of inches, and all essentially the same shape, barring tiny details. In every case, the blade was held onto the hilt with single simple round wooden peg. The most significant difference in shape I could see was that some of them had a more pronounced angle in the blade at the point it met the hilt. As far as the eye could tell, however, they were all functionally the same. The tiny variation in size could be accounted for by the individual personal preferences of the original owners.
I was allowed, in fact encouraged, to pick them up, draw out the blades, and to try swinging them about. This was very informative. Here is the main thing I have to say about katanas: though they vary in appearance very little, they vary enormously in handling. Their balance varied about as much as it is possible for it to vary. Some were dirty great cleavers, with heavy blades, and a centre of gravity around the centre of the blade. Others were tip-heavy, which would be good for delivering a powerful blow with little movement, or for parrying heavy blows. Others were very hilt-heavy, which would be useful for fast parrying of light blows but which would take the punch out of blows delivered. Some were thin and whippy, others very rigid. Clearly the way they were made would have a marked effect on the way they were used.
There were periods when one style of katana was the most preferred kind, and so presumably one style of use dominated, but individual preference still had the power to determine the balance of the weapon. I'm afraid I cannot give you a breakdown of dates and balance types.
So, bear in mind, when you consider the katana, that some were excellent, some rubbish, some like cleavers, and some more like rapiers.
Here is a video about the noise swords make when drawn from a scabbard. It mentions katanas, and the sort of people who love them too much. Don't take it too seriously.