The sharpness of a katana can vary depending on several factors, including the quality of the blade, the type of steel used, the frequency and intensity of use, and the care taken in maintenance. Generally speaking, the sharpness of a katana will diminish over time with regular use.

During use, the cutting edge of a katana can gradually wear down and become less sharp due to contact with various materials, such as targets, armor, or even other blades. This process is known as edge degradation. Additionally, microscopic damage and dulling can occur through regular cutting and impact.

The rate at which a katana loses its sharpness can vary significantly based on the factors mentioned above. For example, a katana used for frequent cutting exercises or combat training may require more frequent sharpening compared to a katana used primarily for display purposes.

Regular maintenance, including proper cleaning, drying, and oiling, can help preserve the sharpness of a katana for a longer period. However, even with diligent care, regular sharpening may eventually be necessary to maintain the desired level of sharpness.

It's worth noting that the sharpness of a katana is not a permanent state, and it requires periodic attention and maintenance to keep the blade in optimal cutting condition.

In summary, the sharpness of a katana will diminish over time with regular use due to factors such as wear, impact, and microscopic damage. The rate of sharpness loss can vary based on several factors, and regular maintenance and occasional sharpening are typically necessary to maintain the desired cutting performance.