HANIKU, HIRANIKU (surface meat)
The edge surfaces of  Japanese swords are convex or "bevel" ground.
They can be finely bevelled or heavily bevelled, that is, less or more rounded in profile.
The Japanese concept for this is "Hiraniku" and literally means "edge or surface  meat". Hiraniku is an important characteristic of  Japanese swords.
A sword with good "meat" (Niku) has a robust and strong edge. In blades with little or no hiraniku, the edge is weaker. The degree of Hiraniku largely dictates the blades cutting power.
HANIKU = The meat or bevel of the cutting surface.
HIRANIKU = The meat or bevel of the whole cutting surface.

HA-NIKU or HIRA-NIKU, these two words have almost the same meaning. Ha-niku tends to mean the meat in the hamon area, and Hira-niku tends to mean the meat of the whole cutting surface.
A cutting surface with full meat (well shaped)
The cutting surface is full of meat, so the cutting edge is tough.
Good for taking on armour.

A flat cutting surface (poorly shaped)
The cutting surfaces are flat, so the edge is delicate.
Good for bare skin.

Be careful. In the showroom window, blades with flatter surfaces look shiny and highly reflective.
Because of this, one famous polisher removes the bevel meat from healthy blades simply to make them aesthetically pleasing.
When you hold one of these blades, you'll be disappointed by their poor shape.
Sometimes a lattice window can help to study the surface meat.

KISSAKI is the tip part of the blade.
Its form is very important.
The meat must be maintained from the yokote to the very tip of the blade.
(YOKOTE = The vertical line that distinguishes the kissaki from the rest of the blade.)

Examples of well shaped kissaki
I'm trying to show their shape with these contour lines. Imagine them as surfaces.

An example of bad shaping
At a glance, the next example appears well formed, but it includes serious problem in fact.
The meat becomes thinner toward the very tip.

Such shaping is good for display or in pictures, but if you held the blade you would be disappointed by the poor surface at the kissaki.
Be careful !  One famous polisher advises converting blades with good kissaki surfaces to the poor form simply because they are better for display.

To the left "A" is a well shaped kissaki. The edge meat is maintained from the yokote line to the tip. This example has a high shinogi line. Sometimes a blade shaped like this can make the top of kissaki small.
To the right "B" is a destroyed kissaki. The kissaki "A" was re-shaped to the kissaki "B". The bevel meat was ground off to make the kissaki look wider.
Don't mistake the lines of a blade for its' shape. In other words, if a blade is formed with neat and sharp lines, it does not necessarily have a good shape. A blade is not a flat drawing. A blades' shape has to be appreciated as three dimensional. It is defined by properly constructed surfaces.
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