The kubikiri (kubigiri) is an unusual form for a Japanese sword (tanto). On a kubikiri, the cutting edge is on the inside curvature; most are of the kiri-ha shape and have no kissaki (point). There were several possible uses for the kubikiri. The term "kubikiri" is traditionally translated as "head cutter" or "head taker". This style of sword (tanto) was carried by attendants to high ranking samurai whose job was to remove the heads of dead enemies as "trophies of battle". While this usage was undoubtedly real in ancient times, by the Shinshinto Era (the period of this sword), the kubikiri was largely a ceremonial sword used as a badge of rank. Some people also call this style of sword (tanto) a "doctor's knife". As the kubikiri had no point (kissaki), it could not be used offensively and was therefore carried by those persons of stature who were entitled to wear a sword, but who were "non-combatants". There is another school of thought that says these style tanto were made for daimyo and high ranking individuals as tools for trimming bonsai. Whatever the usage, this style of tanto is relatively rare in Western collections.
The signature (mei) reads: UNJI UNSHO RYONIN TSUKURU KORE (Unji and Unsho together made this) This mei may be an example of a signature which is possibly not that of the swordsmith. The mei may be, in this case, a political statement of support for the restoration of the Emperor. The mei of Unji or Unsho may be intended to be a dedication to the Emperor and/or Imperial Household. It may also be an anti-Tokugawa (anti-Shogunate) statement. The original Unji and Unsho smiths worked in the early 1300's and made swords for the Emperor Go-Daigo, whereas this blade is most likely of the Shinshinto period. No smiths with the names Unji or Unsho have been documented, to my knowledge, from the Shinshinto period.
Tanto in koshirae simulating a folded Japanese fan are not particularly uncommon. Most have rather low grade blades, although some good quality blades are found mounted in this manner. Legend has it that this style of mounting was used by women and retired samurai as well as doctors, monks and others who did not wish to appear to be carrying a weapon. Fan style mounts were also widely produced in the late 19th and early 20th Centuries as tourist items. The majority of these have poor quality blades.
Ken are one of the rarer styles of tanto. Ken have double edged blades and were mainly made as Buddhist ritual implements although it is not uncommon to find them mounted and used as tanto. Some ken style tanto were made from cut down yari. Ken style tanto were made in Koto, Shinshinto and Gendai eras; but few were made during the Shinto period (few tanto of any style were made during the Shinto era). Ken blades may have parallel edges or double concave shapes as above. Some of the top sword smiths in history made ken as offerings to various temples. It is not uncommon to find ken with a vajra (double thunderbolt) style hilt in keeping with their use as Buddhist ritual implements.
Yari (Japanese lance heads) are occasionally found mounted as tanto. The tang (nakago) is drastically shortened to fit into a tanto size tsuka (handle). This means that if the yari was originally signed by the swordsmith, that the signature (mei) is most likely lost. Small yari tanto were sometimes carried as dirks (kwaiken) by women or as armor piercing tanto by samurai. Yari tanto will normally have a triangular cross-section as distinct from ken tanto which have a diamond cross-section. Also yari tanto will have a reduced "shoulder area" where the blade enters the tsuka and normally have no habaki (blade collar). Yari tanto vary in quality. Some were made by swordsmiths and will have hada and hamon, others were mass produced for foot soldiers and have no hamon. The hi (groove) on the flat side of the yari will possibly be colored with red lacquer.
Single shot pistols in tanto koshirae are relatively rare. The matchlock gun was introduced into Japan in the 15th Century by the Portuguese. The Japanese readily adopted the gun as a weapon of both military combat and personal defense although it was considered not to be a weapon worthy of the samurai. Pistol tanto were carried as weapons of personal defense. Most pistol tanto date from the late 18th and 19th Centuries. They are single shot pistols with fold down triggers and were not very accurate. Some scholars consider them a fad item for the wealthy of the period.
Hachiwara are not actually tanto as they are not a sword, but rather a forged iron bar designed as a defensive weapon against swords. They are sometimes called sword breakers or helmet breakers. The blades are normally of square cross-section with a hook next to the grip, approximately 12 to 15 inches in length. The mounts are commonly of carved wood or carved cinnabar lacquer. Some hachiwara were made by noted swordsmiths and may be signed.
Information taken from http://japanesesword.homestead.com/files/nihonto.htm