Natural wood is more sensitive to humidity swings than lacquered wood, so storage environment matters. Keep the saya in a room with stable relative humidity between 40–60%. Every few months, apply a thin coat of food-grade mineral oil or traditional choji oil with a soft cloth, wiping along the grain and buffing off the excess. This prevents the wood from drying out and developing hairline cracks. Avoid placing the saya in direct sunlight for extended periods, as UV exposure can bleach the grain and cause uneven fading. If you display the katana on an open rack, a quick wipe-down with a dry microfiber cloth once a month removes dust that can trap moisture against the surface.