The "tsuba" is a handguard or guard that is specifically designed to protect the hand of the wielder on a katana or other traditional Japanese swords. It is a circular or sometimes geometrically shaped metal or alloy plate located between the blade and the hilt (handle) of the sword.

The tsuba serves several important functions:

1. Hand Protection: The primary purpose of the tsuba is to provide a protective barrier between the blade and the hand of the wielder. It helps prevent the opponent's blade from sliding down and making direct contact with the wielder's hand during combat, reducing the risk of injury.
2. Balance and Control: The tsuba contributes to the overall balance and control of the katana. It helps distribute the weight of the blade and influences the sword's center of gravity. By adjusting the size, shape, and weight of the tsuba, the sword's handling characteristics can be fine-tuned to suit the wielder's preferences and combat style.
3. Style and Aesthetics: The tsuba is often an ornamental and artistic element of the katana. It can feature intricate designs, engravings, or inlays, reflecting the craftsmanship, cultural motifs, or personal symbolism of the swordsmith. The tsuba is an opportunity to enhance the overall visual appeal and individuality of the katana.

Tsuba designs can vary greatly, ranging from simple and functional designs to highly elaborate and decorative works of art. Different historical periods, sword schools, and personal preferences can influence the style and motifs depicted on the tsuba.

In addition to its functional and aesthetic roles, the tsuba can also act as a spacer, keeping the hand from slipping onto the blade during vigorous sword movements. It contributes to the overall safety, control, and effectiveness of the katana in combat.

It's worth noting that tsuba-like handguards can also be found in other traditional Japanese swords, such as the wakizashi and tanto. The tsuba's design and dimensions can vary between sword types, historical periods, and cultural influences.