Here is an article about certain Tanto that were used for beheading an enemy . One of the many weapons used for beheading .
The kubikiri (kubigiri) is an unusual form for a Japanese tanto. On a kubikiri, the cutting edge is on the inside curvature (extreme uchi-sori); most are of the kiri-ha shape and have no kissaki (point). There were several possible uses and many "tall tales" about kubikiri. The term "kubikiri" is traditionally translated as "head cutter". This style of tanto may have been 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 possibly real in ancient times, in later eras it would have been largely a ceremonial sword used possibly as a badge of rank. These are also referred to as bokuwari tanto which means wood splitter. They may have been used to cut charcoal for sumi or incense for either the tea ceremony or incense game. Some people also call this style of tanto a "doctor's knife". As there is no point (kissaki), it supposedly 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". It is also possible that this style of tanto (hanakiri) was made for wealthy individuals as tools for trimming bonsai and doing garden work or ikebana, similar to the saw tanto below. Another possibility is that they were used by forestry officials for taking trimmings or cuttings for propagation. Tanto of this type date from the Meiji to early Showa eras, a period when most sword makers and koshirae artists had little work making traditional swords. Whatever the usage, this style of tanto is relatively rare in Western collections. Here is a good link for questions about Japanese history and any questions you may have about japanese anything.
http://forums.samurai-archives.com/...answered&sid=45b80dbebb8733c946d9f331931379f8