Ōdachi, also known as nodachi, were long Japanese swords that were primarily used by foot soldiers and warrior monks during certain historical periods. The specific use and purpose of the Ōdachi can vary depending on the time period and context. Here are some common applications and functions associated with Ōdachi:

1. Battlefield Use: Ōdachi were often employed in open-field battles where their long reach and sweeping strikes were advantageous. Their extended reach allowed the wielder to strike multiple opponents from a distance, providing an advantage against cavalry or multiple enemies.
2. Anti-Cavalry Weapon: Due to their length and cutting power, Ōdachi were particularly effective against mounted opponents. The long blade could reach over the protective armor of mounted warriors, making it easier to deliver devastating strikes.
3. Symbol of Prestige: Ōdachi were also used as ceremonial or symbolic weapons, representing the authority and status of high-ranking samurai or warrior leaders. They were sometimes carried by officers or displayed during processions to showcase power and social standing.
4. Rarely Used in Dueling: Due to their size and specialized nature, Ōdachi were less commonly used in one-on-one duels. Their length and weight made them less maneuverable in close-quarters combat compared to shorter swords like the katana or wakizashi.

It's important to note that the use of Ōdachi diminished as the focus of warfare shifted to more confined spaces and the advent of more specialized battlefield weapons. As a result, Ōdachi gradually fell out of favor and became more associated with ceremonial or historical contexts. Today, Ōdachi are often appreciated as fascinating relics of Japan's martial past and are sometimes replicated or used in martial arts demonstrations.