Biography
Your character is a barbarian, and they mean business. They aren’t afraid of going unprotected in sword on sword combat, exposed to the parasites and hazards of the Hungry Jungle or being Exposed to the Elements of the Grim Up North, but your culture is very noble with reasonable modesty standards rather than being complete savages. So you have your character hunt the nearest wildcat to fashion a loincloth.
The loincloth is a lower body garment that covers the essentials, while leaving the rest completely bare for things like heat or mobility. It is usually seen in stereotypically primitive cultures or hot climates where armor is more rare, but even in a stricter culture where it is only an undergarment in a stricter culture, it still will often be worn for athletic activities like martial arts or swimming.
Design varies, but the cloth usually has coverage underneath between the legs it’s implied otherwise, where either Magic Skirt or Rule of Sexy takes over. The style can also very widely. With [[Walking Swimsuit Scene briefs]{ indicating practicality, while long flowing cloths over the legs with open sides can indicate the class of a Vestigial Empire or ancient culture, but the most iconic version is the tattered unkempt barbarian version, usually including a small flap to catch the wind in the front and back.
While often crafted in cloth or plants in Real Life, the barbarian loincloths are usually Crafted from Animals, (per Rule of Cool), typically something dangerous like a big cat (usually a leopard) or a bear that a Noble Savage would have won in fair honorable combat, obviously Killing in Self-Defense because Hunting Is Evil. Most authors handwave the origins of the outfit entirely. Wearers include the jungle hero or heroines, who tend to be Surefooted Barefooter\s, and the Barbarian Heroes tend to have Boots of Toughness. The both characters have exceptions, but such exceptions can feel out of place aesthetically.
Usually this trope justifies a Walking Shirtless Scene for males. If the wearer is an Action Girl, expect Hollywood Beauty Standards to usually apply, but if Rule of Cool is present, expect, an unkempt Amazonian Beauty. In either can, she almost always has either a matching bikini top or Diamonds in the Buff to cover the rest.
Though appearing impractical, there a surprising amount of Truth in Television here. Whether it be the Celtic soldiers the leotards of the circus, many societies wore less for physically demanding things, including hunting, martial arts, and combat. Of course the latter tends to be a head scratcher in comparison to armor. For the Celts, it wasn’t justified as the upper classes still had armor, but one would not last long wearing plate armor in the Hungry Jungle due the the heat it generates, so most subsaharan cultures focused more on mobility with a shield, making full covering armor much more rare.
Of course this trope was primarily came from the appeal of the leotard clad daring feats of the circus in the early 20th century, but it wasn’t til Tarzan and John Carter started wearing them and they appeared on the cover of every other pulp magazine, that it became synonymous with adventure and exoticism. Once Conan dawned the briefs the rest was history.
The main meat and point of interest of this trope is the nobility of the wearer. While it may look Stripperiffic, the story will often subvert these aspects. The barbarian usually comes from a culture where Our Nudity Is Different, and even might be a Celibate Hero, while Jungle Princess is usually a Chaste Hero and an Earthy Barefoot Character. These characters are rarely promiscuous, but rather courageous to the elements (some are even homeless) and humble contrasted with wealthier societies. They prefer simplicity and skill to heavy armor or what they can craft to expensive clothes. Thus, the term “modesty” takes on a completely different definition in relation to them.
A Super-Trope to Fundoshi. The Fur Bikini often functions like this. See also Surefooted Barefooter, which is common for jungle characters with this trope.
Compare Pelts of the Barbarian.