In the Ranma ½ manga, several of the girls (Akane, Ukyo, Ranma-onna) wear sarashi, bleaching cloth, wrapped tightly around their midriffs and chests when trying to hide the fact that they are female. A sarashi is a long, strip of cloth, most commonly made of thick cotton. It used to be worn by samurai under their kimono, to make it harder to be wounded in sword fights (amongst other reasons, after all it is a long cloth strip that can be used for many purposes, such as make shift bandages). It is considered a symbol of toughness and until fairly recently masculinity in Japan. Yakuza and yankii (youth gangs) wore sarashi until fairly recently because of the symbolism. Which is a bit strange when you consider they were and are also used by pregnant women to support the stomach.
I do not recall reading many fanfics in which characters wear sarashi or breast wraps, even in period pieces such as the feudal period, when bra's were yet to be invented. While the occasional Ranma fan fic will have Ukyo wearing one it is rare for any other character to do so. Ukyo is shown to wear one in her intro while she is dressing like a guy, so it might get remembered more often but I still don't get why other characters don't. Most specifically Ranma since they can, and are, worn by both males and females.
While looking up information on sarashi I happened upon a poem/song. It can be found at The International Shakuhachi Society website.