Long-term storage of a red blade manganese steel katana requires attention to two main threats: moisture and contact abrasion. Store the piece horizontally on a katana stand or vertically in its saya with the edge facing upward in the traditional Japanese manner. Apply a thin layer of choji oil (a light mineral oil with clove scent traditionally used for Japanese blades) to the blade surface every two to three months using a soft, lint-free cloth - this forms a barrier against humidity and slows oxidation. Avoid storing in leather-lined cases for extended periods, as leather can retain moisture and off-gas acids that affect the blade finish over time. A humidity level between 40-50% is ideal. The saya interior should also be checked occasionally to ensure no moisture or debris has accumulated inside.