A kodachi is a traditional Japanese sword that is shorter than a standard katana but longer than a tanto. It typically has a blade length between 45 and 60 centimeters (18 to 24 inches). The term "kodachi" translates to "small sword" or "short sword."

Historically, the kodachi was used as a secondary weapon or as a backup to the main weapon, such as a katana or a spear. It was commonly employed in close-quarter combat, particularly in situations where a longer weapon would be cumbersome or unsuitable.

The main purposes of the kodachi were similar to those of other Japanese swords:

1. Self-Defense: The kodachi was a versatile weapon for personal protection and self-defense, offering maneuverability and quick strikes in confined spaces. Its shorter length allowed for swift draw and strikes in close-quarters combat.
2. Dueling: Kodachi were occasionally used in duels or as ceremonial swords. Samurai warriors who specialized in dual-wielding techniques or preferred a more agile weapon would often choose a kodachi as one of their blades.
3. Training: Kodachi were used for training purposes by samurai to develop their swordsmanship skills, techniques, and speed. The shorter length and lighter weight made it suitable for practice and sparring.

It's important to note that the usage of the kodachi varied depending on the historical period, region, and the specific martial traditions or styles employed. The kodachi was not as prevalent as the katana or the tanto in Japanese military warfare, but it played a role in certain contexts and specialized combat techniques.

In modern times, the kodachi is sometimes replicated or imitated in martial arts training or as a collectible item. Martial artists may practice techniques specific to the kodachi or utilize it as a training tool for certain sword-fighting styles. Collectors may acquire kodachi replicas as historical artifacts or decorative pieces.