As I recently wrote, translating Dungeons and Dragons as a game into another medieval cultural setting can be a challenge. As someone who writes independent adventure modules for a Japanese-inspired setting on DMS Guild, I appreciate this point a lot. Nowhere is this more so a challenge than armor.
Originally, when I first made this setting, I tried using custom armor types, but in the end I found them of limited use, and hard to keep track in my head as a DM, so in the end I decided to compromise and make Japanese armor 1:1 equivalent to Western armor types where feasible. This might not be preferred by purists, but a busy DM has to work on limited time and resources, so I decided this way I could preserve the “flavor” of Japanese armor, while keeping the mechanics simple.
Dungeons and Dragons lists several kinds of armor from simple leather and hide armor, to plate armor worn by knights. Medieval Japan similarly had various types of armor used in warfare, including armor more familiar to a Western audience, but also some armor types that don’t have an obvious Western equivalent. This website, the Costume Museum of Japan, has great visuals on Japanese armor, if you would like to see many examples. I will be linking specific examples from the website throughout this page for easier visuals.
Anyhow, having done some homework, both in English and Japanese, I will try to breakdown the various armor types used in Japanese warfare and determine what an equivalent might be. This is just one DM’s interpretation, and your mileage may vary, but feel free to use the suggestions here and adapt as needed.
Basic Comparison
These charts are similar to the ones found in the Player’s Handbook but I left out certain armor types that are either seldom used (e.g. ring mail) or obviously the same across cultures (hide armor), or just not worth providing conversion for. The rest are listed here. If you’re looking for a quick-and-easy reference, please start here.
| Light Armor Name | Japanese Equivalent | AC | Stealth |
| Leather | 練革 (nerigawa) | 11 + Dex modifier | — |
| Studded Leather | 亀甲 (kikkō) | 12 + Dex modifier | — |
| Medium Armor Name | Japanese Equivalent | AC | Stealth |
| Chain Shirt | 腹当 (hara-até) | 13 + Dex modifier (max 2) | |
| Scale Mail | 腹巻 (haramaki) | 14 + Dex modifier (max 2) | Disadv |
| Breastplate | 銅丸 (dōmaru) | 14 + Dex modifier (max 2) | |
| Half Plate | 銅当世 (dō-gusoku) | 15 + Dex modifier (max 2) | Disadv |
| Heavy Armor Name | Japanese Equivalent | AC | Min. Strength | Stealth |
| Chain Mail | 畳具足 (tatami-gusoku) | 16 | 13 | Disadv |
| Splint | 大鎧 (ōyoroi) | 17 | 15 | Disadv |
| Plate | 当世具足 (tōsei gusoku) | 18 | 15 | Disadv |
Let’s break these down in detail below…
First, O-sodé, Not Shields
One feature of Japanese armor and warfare is that shields were not used at all, and are simply not found. On the other hand, many of the armor types you see below came with an optional component called ō-sode (大袖, lit. “big sleeves”) which were large, square-shaped shoulder-guards that covered the shoulder-blades, upper-arms and such. They give some additional protection, while allow both hands to be free, so I converted them into a kind of “light shielding” like so:
- Type: Shield
- Cost: 10 gp
- Weight: 6 lbs
An ō-sode is an extra shoulder-guard made from lamellar metal (older versions) or metal plate (newer versions) and is worn over both shoulders, toward the back. Players who are girded with ō-sode gain some additional shielding while keeping both hands free.
| Name | Cost | Armor Class | Strength | Stealth | Weight |
|---|---|---|---|---|---|
| Ō-sode | 10 gp | 1 | — | — | 6 lbs |
O-yoroi: splint mail
The 大鎧 (ōyoroi) armor shown here is the most iconic in Japanese culture, and was especially common during the earlier Kamakura and Heian periods of Japanese history (8th-13th century). It is a kind of heavy, box-shaped armor that includes several large, overlapping plates around the shoulders, leg greaves, helmet, and of course the torso. This is definitely a larger, more heavy armor and due to its interlocking “plates”. It was well-suited for horseback riders who attacked with spears and bows, but for hand to hand combat on the ground.
This is one of the harder ones to pin down in Dungeons and Dragons, because the shape and design have no obvious analog in medieval European armor, but for now I’ve tentatively called it splint mail due to its heavier, full-body design, and interlocking plates.
Domaru: breastplate
銅丸 (dōmaru) is another armor type from the same period, comprised of lamellar, but has a more tight-fitting, yet flexible design. An example can be seen here. Dōmaru is similar in design to the ōyoroi above, but covers only the upper half of the body, yet has improved maneuverability.
This is another one that’s hard to pin down and convert to European-style armor, but it does provide fairly comprehensive coverage of the upper body, even if still somewhat heavy and clunky. Breastplate is as appropriate as any armor type that I can think of.
Haramaki: scale mail
The haramaki (腹巻) was a kind of armor that was often used by foot soldiers and lesser samurai compared to the expensive ōyori. As with dōmaru, it is mostly comprised of lamellar scales, and covers the torso only, but between its limited coverage, scaly design and cheaper price, I am tend to convert this to scale mail in Dungeons and Dragons.
Hara-até: chain shirt
An even lighter, simpler design from the same period is the hara-até (腹当) which covers less of the body, but like the examples above, offers flexibility. At first glance, this seems like a breastplate, but with the pieces stitched together in a lamellar format, chain shirt seems more appropriate. I went with chain shirt in this case.
Tatami Gusoku
From here on out, we move away from the older lamellar designs to gusoku (具足) design that was used in the later 15th century Warring States period onward. These designs may have been influenced by recent contact with Western explorers, as well as changes in warfare due to the introduction of firearms and other changes in tactics.
The 畳具足 (tatami-gusoku) is a lighter-weight, fold-able armor that was often used by foot soldiers, guards and lower-ranking samurai. The word tatamu (畳む) means to fold. Anyhow, this armor definitely looks like chain mail in the Western sense, so this is a pretty easy choice.
Tosei Gusoku: full plate
Another iconic form of armor invented in the 15th century Warring States period the 当世具足 (tōsei gusoku). The term tōsei (当世) by the way means “modern” as during this period it was newer technology compared to the older ō-yoroi armor of centuries past. You can see an example of it here. This replaces lamellar scales with larger, form-fitting metal plates, and definitely resembles full plate armor. This armor is full-body, completes with metal greaves, helmet, the works.
It is also the kind of armor that only samurai warlords and other high-ranking warriors could realistically afford.
Also, while “half-plate” armor wasn’t necessarily common, it’s reasonable for a player character to purchase only the upper half of this armor, which I believe is called 銅当世 (dō-gusoku).
What About Leather Armor?
I tried many times to look up what leather armor was in Japan, and the answer was surprisingly tricky. Many of the smaller, cheaper armor types listed above could be made using either iron or leather (called nerigawa 練革), especially older lamellar armor. So the coverage and shape would be the same, but the material of the scales would differ.
So, how would that work in D&D?
For our purposes, we can probably just call basic leather armor nerigawa, or even just “leather”.
On noteworthy example is kikko (亀甲) armor. Normally, kikko armor is treated as brigandine armor, but the design is basically a leather backing with small, hexagon-shaped metal scales, so that tends to roughly fit my definition of studded leather.
Conclusion
The examples shown here, and the attempt to map them to 5th-edition Dungeons and Dragon armor is, at best, a rough guide and should be taken with a grain of salt. In the end, a DM may decide to forgo the Japanese terms entirely and just use Western-English terminology while the appearance of the armor might better match Japanese flavor and appearance. On the other hand, some armor such as ō-yoroi and tōsei-gusoku are iconic armor and probably worth special-mention in a Japanese-setting campaign. As the DM you are empowered to make appropriate decisions that make the experience fun for your players.
Either way, I wish you good luck and happy adventuring!
P.S. It’s likely that I will be updating and modifying details as time goes on, so please feel free to check back here for updates.
Gleanings in Buddha-Fields 
