Today I'm going to introduce you to a sugata thats both a little bit strange and also, in my eyes, exceedingly historically important when it comes to the evolution of the Japanese sword, a style known as Kissaki-Moroha-Zukuri. This is a geometry thats more popularly known by it's namesake, "Kogarasu Maru" or "Little Crow", which was a famous tachi reputed to have been created by the equally famous swordsmith Amakuni Yasutsuna in the 8th century. This means that when we talk about Kogarasu Maru, we aren't actually talking about a geometry but rather one specific instance of it that all others seem to have become to be known as. If that isn't flattery I do not know what is.
The original version of this sword was shaped like a Chinese Ken or a European broadsword but whereas one side was fully sharp, only the tip on the other side was sharpened in the same fashion. Normally there would be a groove on the unsharpened part called "koshi-hi" and also a thin groove which would run the length of the blade straight up the centre called "soe-hi".
Why was the sword shaped in this way? Well in order to answer that question we have to skip back a few hundred years to around 700AD when the swords produced in Japan were almost identical to those being made in China. Indeed the import of swords and steel from China was commonplace. It was one such sword that served as the inspiration for the "moroha zukuri" style sword that we picture every time we hear the name, but like all other swords of those times, it was straight.
This changed however around the fall of the Tang dynasty, when Japan truly seperated the evolutionary path of their swords from the Chinese and started redefining the geometry and dimensions as well as truly kicking their smelting and heat treatment techniques into overdrive. This heat treatment technique of course is the factor that would pull the sword into the iconic curvature theyre known for today.
The picture above is of a tanto in the same geometry, but what is interesting is that apart from the curvature, the relative dimensions are closer to the dimensions of the ancient chinese swords when it comes to the bladed area on the back. This sharpened area got longer as time went on and strangely enough this continues with todays modern reproductions. Aesthetics play as heavy a hand today and more garishly than they did back then when these things were weapons of war.
So this back edge, it's sharp right? yep, and from a modern day martial arts point of view, especially when it comes to noto and the way the sword is drawn across the hand before resheathing means that it can be a pain to use, sometimes quite literally. Traditionally the back half of the blade was sharpened which makes the resheathing process in the usual sense somewhat problematic. Having said that, manufacturers of this particular style nowadays have made a few changes in the name of practicality and cost, the most obvious ones being mounting the sword as katana rather than tachi as well as leaving the back of the blade shaped but unsharpened.
This relief or false-edge as its sometimes called, on the back side of the blade also serves another purpose be it intentional or not and that is to make it less top heavy. Having the point of balance for this sword closer to the tsuba means that it feels lighter and more manipulable in the hand, similar some say to the Unokubi Zukuri.
So, now you know a little about this very uncommon style maybe you should give it another look. Most modern interpretations of course do not do it any real justice but they can be pretty nonetheless. The real intrigue in my humble opinion comes from the way it joins together two countries in history that most do not even realise had such intertwined beginnings.