Kaiken (dagger)

A kaiken (懐剣) is a 20–25 cm (7.9–9.8 in) long, single or (very rarely) double-edged Japanese knife[1] usually without ornamental fittings housed in a plain but lacquered mount.

Women carried them in their kimono either in a pocket-like space (futokoro) or in the sleeve pouch (tamoto)[2] for self-defense and for ritual suicide by slashing the veins in the left side of the neck.

[5] The kaiken was also carried concealed in its shirasaya by the lower classes who were not permitted to wear swords, in particular by criminals in the Edo period.

In modern Japan, a kaiken is worn as a traditional accessory for the gyōji (referee) in sumo matches for the highest ranks.

No one legally wears or carries a kaiken today in Japan, as this is a violation of the Gun and Sword Law.