Katana

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Name	katana
Appearance	samurai sword
Damage vs. small	1d10
Damage vs. large	1d12
To-hit bonus	+1
Weapon skill	long sword
Size	one-handed
Base price	80 zm (+10/positive enchant)
Weight	40
Material	iron

A katana does d10/d12 damage against small/large monsters, with a +1 bonus to hit. When unidentified, it appears as a samurai sword; samurai start with one. The sole artifact katana is Snickersnee.

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.

A katana will not turn into the Excalibur if you dip it into a fountain. Don't degrade your weapon.

Generation

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. This makes getting one for most classes largely dependent on random chance.

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 attain one.

Randomly spawned stores are another—though by the time the player is worrying about attaining 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.

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.

Trivia

Despite them making for the best long sword in the game, historically speaking, katanas were no better than an equivalent European sword. In the same era, while many katanas were better than European broadswords, this was simply because katanas were not mass produced (recall that Europe was often at war, and Japan quite isolated); in fact, due to poorer quality steel in Japan, in a fairer comparison (non-mass-produced European sword) katanas were actually worse. This is not a fault of NetHack, per se, as canonical Dungeons and Dragons from which NetHack is based.

It could be said, however, that due to the large number of soldiers in the game, the long swords in NetHack are indeed most likely mass-produced. Furthermore, the +1 to-hit may be a nod to D&D, in that that is the exact bonus given to masterwork equipment. Although this still does not account for the fact that the stereotypically better Elven equipment, the Elven broadsword, is still worse (on average) than a katana.

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	$\frac{1+10}{2}+2=\bold{7.5}$	$\frac{1+12}{2}+2=\bold{8.5}$	$\frac{1+10}{2}+2=\bold{7.5}$	$\frac{1+12}{2}+\frac{1+4}{2}+2=\bold{11}$
Blessed katana +7	$\frac{1+10}{2}+2+7=\bold{14.5}$	$\frac{1+12}{2}+2+7=\bold{15.5}$	$\frac{1+10}{2}+2+7=\bold{14.5}$	$\frac{1+12}{2}+\frac{1+4}{2}+2+7=\bold{18}$
Blessed katana +9	$\frac{1+10}{2}+2+9=\bold{16.5}$	$\frac{1+12}{2}+2+9=\bold{17.5}$	$\frac{1+10}{2}+2+9=\bold{16.5}$	$\frac{1+12}{2}+\frac{1+4}{2}+2+9=\bold{20}$

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.

Encyclopedia entry

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.