|Damage vs. small||1d10|
|Damage vs. large||1d12|
|Weapon skill||long sword|
The only differences between katanas and long swords are the +1 bonus to hit and the katana's 1d10 damage vs. small (as opposed to 1d8 for a long sword). Because the katana is the most damaging non-artifact weapon to use the long sword weapon skill, it is often a desirable off-hand weapon for two-weapon combat.
Katanas are rare, very rare. In fact, only 4 in 1000 (0.4%) of all randomly spawned weapons will be a katana, making it the seventh rarest weapon in the game—a slot it shares with the lance, among several others less notable. This makes getting one for most classes largely dependent on random chance.
As noted above, Samurai start with one in their initial inventory, and a Samurai hoping to #twoweapon should generally keep their original, as they're quite rare; should anything happen to it, it's possible to get another during the samurai quest. Bones from a Samurai are another chancy way to get a katana. Otherwise, for all classes, it may be worth spending a wish to get one. While there are several monsters that spawn with a special chance of a katana in their inventory, they're all located on the samurai quest. Considering that reverse genocide never spawns monsters with items, no help there. And one shouldn't waste genocide scrolls attempting.
One good place to look is the Castle stores—collectively, there is a decent 5.46% chance of finding one there. Death drops are another small chance of getting a katana—in Gehennom, where weapons are spawned with about 20% of all items, there is about a 0.0136% chance that a given monster will have a katana in their inventory. At such minuscule odds, however, one must slay ~2115 creatures to be even 25% confident to pry one from their cold, dead, slimy hands.
Randomly spawned stores are another—though by the time the player is worrying about acquiring one, they've likely gone through all the stores that the Dungeons of Doom has to offer. Late in the game, Orcus Town in particular has a small chance of having a katana spawned. The two general stores have a collective 3.15% chance of having a katana, assuming there are no mimics.
If the game has a portal to Fort Ludios, each soldier has a guaranteed weapon, as well as the usual death drops. The 87 Yendorian army members there have a trivial ~0.59% chance of spawning a katana to plunder through death drops alone. However, the large number of weapons otherwise spawned may make it possible to polypile for the katana. To be 50% confident to attain a katana, one need polymorph 172.94 items—easily do-able with the 87 weapons assured to be there.
The table below relates the chance of getting a katana, assuming all the weapons are placed onto one pile, are uncursed, and the player has maximized their luck, so as to lessen the chance of hostile iron golems. The confidence given is "overall," or "cumulative," meaning that if the player does not get it the first time, the odds do not increase, magically or otherwise.
|Polyfodder left (avg)||87||65.25||48.94||36.70||27.53||20.65||15.48||11.61||8.71|
|Total items polymorphed||00.00%||66.25||114.19||150.89||178.42||199.06||214.55||226.16||234.87|
While the katana has been heralded continually as one of the best if not the best blades of all time, and is without a doubt superb against an unarmored or otherwise lightly armored enemy, it is not fit against heavy armor such as chainmail seen in Europe due the fact that a katana is made for slicing and slashing, and not stabbing, which is predominately what European swords were suited for. That said, the craftsmanship of katana is second to none and it is without a doubt a superior blade for the purposes that it was produced against the armor that it was facing, and the steel a bit better due to better forging and techniques and so forth,  but in the situation of chainmail or some other types of European armors, a European longsword design would have been better for the job in that particular situation.
Average damage calculation
We assume the player has expert skill in long sword, which gives a +2 damage bonus. A blessed weapon deals 1d4 extra damage against demons and undead. The worst case scenario is against a small, non-undead, non-demon. The best case scenario is against a large undead/demon monster.
|Weapon||Against regular small monsters||Against regular large monsters||Worst case scenario||Best case scenario|
|Blessed katana +0|
|Blessed katana +7|
|Blessed katana +9|
Despite the inclusion in the above table, attempting to enchant a katana to +9 is generally a very bad idea, as they're quite rare.
The katana is a long, single-edged samurai sword with a
slightly curved blade. Its long handle is designed to allow
it to be wielded with either one or two hands.