Or, “clearing my notes.”
Japanese scholars talk about three sword-making periods:
- the Shintō (“new sword”), the era of the daishō, which corresponds closely (but not exactly) to the Edo period (a.k.a. the shogunate);
- the Kotō (“old sword”), the period preceding Shintō (the date of transition is usually given as 1596); and
- the Shinshintō (“new-new sword” — I kid you not), from about 1781 to 1876, when wearing swords was prohibited. The reason why it gets its own period is because you could still make and own swords, and craftsmen were freed to make imitations of the Kotō swords.
A fantasy world might reasonably be set in a period like the Kotō, as it was more tumultuous than the shogunate. The three weapons that would be more common are:
- the tachi,
- the tantō, and
- the uchigatana.
To be honest, “tachi” is a term akin to “sword” in the West. At the beginning of the Kotō, the tachi resembled a two-handed Chinese jian, right down to the pommel and hilt designs. (So much so that it’s still debated whether they’re actually Japanese, or whether they’re Chinese imports.) By the end of the period, it looked an awful lot like a big katana — but it wasn’t really used like one, or acted like one. The commonality between all the versions of the tachi was that it was a cavalry sword, for use against targets that weren’t well armored. (At least, as compared to a katana’s opponents.) As a result, it was usually longer, to be able to reach targets from horseback, and didn’t need to be as stiff.
A tachi was worn hanging from the samurai’s waist, edge down (much like a Western cavalry sword), and was typically the back-up to the samurai’s primary weapon, a bow.
The tantō is best described as a dagger. Its blade was generally about a foot long, and wide for a dagger. It proved its use during the Mongol invasion, where stories describe samurai switching to it in the cramped quarters of a ship.
The uchigatana is the transitional sword between the late tachi and the early katana. Basically, it was a short, cheap blade carried by poor samurai and near-samurai as their sidearm. Their main weapon at this point was probably a spear (yari), and they fought on foot. The quality of these swords were so bad that few of them survive to today. That said, it was a more comfortable sidearm than the tachi, which lead to the higher-ups wearing them, and spurring the evolution to the katana. These could come the same lengths as both the wakizashi and the katana.
Lastly, there was the kodachi, which is basically a short tachi. They were about two feet long — longer than a wakizashi, and shorter than a katana — but I don’t know much about their application.
For D&D 5e:
- Tachi; 1d10 slashing damage; Heavy, Two-handed.
- Tantō; a non-throwing dagger. (To be fair, you shouldn’t throw a rondel dagger, either.)
- Uchigatana; 1d6 slashing damage; Versatile (1d8), breaks on an attack roll of 1.
- Kodachi; use the scimitar stat line.