Aikuchi is a form of mounting for Japanese blades in which the handle and the scabbard meet without a guard in between. Originally used on the koshigatana (a precursor to the wakizashi) to facilitate close wearing with armor, it became a fashionable upper-class mounting style for tanto (daggers) in the Edo period.
Small aikuchi tanto known as kaiken became popular with the Yakuza, as they were easy to conceal; however, the most typical user of kaiken were women samurai from the Edo period onwards, who kept it as an emergency and/or suicide weapon.
The dagger was short and it had a cutting edge the length of which was about 23cms. It could serve for self-defense as well as for attacking the enemy by throwing it. This weapon looks similar to tanto, the only difference is that aikuchi does not have a hand guard. It was very popular during fifteenth century and was used mainly during infighting as well as close range grappling. The aikuchi served well for dispatching the enemy when thrown to the ground. The weapon can be easily recognised by the size of its blade as well as by the fact that it had no hilt guard. Aikuchi were also created in a thicker version called yoroi toshi (Japanese for “armour piercer”). Yoroi toshi was a strong dagger able to cut through armor when fighting at a close range.
There was also another type of aikuchi called moroha zukuri (Japanese for “double-edged style”). Its blade length was about 18cm and its blade was sharpened on both sides.
It is considered that the best aikuchi knives were created by the famous Japanese swordsmiths that represented the Osafune school, situated in Bizen province. Nowadays these daggers are considered to be very rare and thus very valuable.
Lucy Lui’s character O-Ren Ishii in Quentin Tarantino’s Kill Bill used a black aikuchi-style katana sword.