Japanese saws require special feather-edge files for sharpening.
For the ryoba, azebiki, anahiki and pruning saws, a 100mm (4") file is required. For the regular dozuki and the very fine teeth in our professional dozuki, a 75mm (3") file is best. A safe-cut file is recommended for those who have not sharpened Japanese saws before.
Depending upon the intensity of use, sharpening once per year should be adequate.