A shirasaya (白鞘), literally “white scabbard”, is a plain wooden Japanese blade mount consisting of a saya (scabbard) and tsuka (hilt), traditional made of nurizaya wood and used when a blade was not expected to see use for some time and needed to be stored. They were externally featureless save for the needed mekugi-ana to secure the nakago (tang), though sometimes sayagaki (blade information) was also present. The need for specialized storage is because prolonged koshirae mounting harmed the blade, owing to factors such as the lacquered wood retaining moisture and encouraging corrosion.
Such mountings are not intended for actual combat, as the lack of a tsuba (guard) and proper handle wrappings were deleterious; as such they would likely never make their way onto a battlefield. However, there have been loosely similar “hidden” mountings, such as the shikomizue. Also, many blades dating back to earlier Japanese history are today sold in such a format, along with modern-day reproductions; while most are purely decorative replicas, a few have functional blades.