The line from the start of the kissaki to the top of it is almost straight.
Such a kissaki is especially called "kamasu-" even if the kissaki is long or short. It looks very sharp.
This type has a little different meaning than other types. Because, this type is an original shape of the kissaki before 14th century. But it is very rare to be found today.
The tip is very sharp and delicate, so it is easy to be broken in a fight. The kissaki line easily becomes round by re-polishing after use. We can see kamasu type only on healthy blades in some old temples or shrines as their treasure. They were put in there before use to celebrate Buddha or god.
=> Uesugi tachi of Ichimonji
Therefore we have to change the image of the kissaki shape when we think about the original in the period of samurai living before 14th century.
After 15th century, most of the kissaki shape is "chu-" and "o-kissaki", never seen "ikubi-" or "ko-kissaki".
"Regarding blade form and samurai culture in the history"
Some type of kissaki is typical in a particular period of time. Of course it comes from practical advantages in the fighting style, but that is not the only reason. The spirit of the samurai culture makes the styles of each period.
Of course, there are various types of blades in every period. We speak about just the typical type of each period.
The late Heian to the early Kamakura period
In the 12th century, the samurai's' status is not so high. They are guards of the nobility. The government never stand without samurai, but they don't have political power. They fight often for the political game of nobilities. And they are longing for the nobility culture.
In the battle field, the main weapon is the bow and arrow, so the armour is heavy and hard. The typical blade style in this period is big fumbari, emphatic koshi-sori, and ko-kissaki. It is elegant for the eyes and good to aim for the openings in the armour.
It is told that such an elegant form suggest the samurai's yearning for the nobility culture. But, most of the blades from that period is very worn. we have to study again if the form is so in its original. (=> Changing of blade shape by wearing)
The early Kamakura period to the middle
At the end of 12th century, samurai get their own government. Officially, it is a guard of the emperor.
Blades become strong and powerful. In other words, thicker and wider.
The late Kamakura period
In the late 13th century, Japan gets attacked by Mongolia twice. Samurai fight very hard and then they have to prepare for the third attack. The period is very exciting and samurai's are united against the next invasion.
In this period the blade with an ikubi-kissaki is typical. The strong blade with ikubi-kissaki is a symbol of the samurai spirit in this age. A short and thick kissaki may be heavy duty.
The Nambokucho period
In the early 14th century, the samurai government is broken and two imperial governments appear. Samurai's fight each other for their emperors. There is no order in samurai society. Each samurai tries to display themselves to emphasize their power.
In this period, large and O-kissaki blades become typical. So also is an artificial wavy hamon and designed engravings. Such a blade is easy for the eyes to feel the power.
The Muromachi, Momoyama, and Edo period
After 15th century, most of the blades have chu-kissaki or o-kissaki. There is no era that has a special kissaki type.
In history, the style of the blade is a fashion of the period. Probably it means the spirit of the samurai culture in the period.
Every blade has a form where the width and the thickness becomes larger toward the tang. In other words, a blade is tapered from the wide base toward the narrow head.
Fumbari is a form that has a large rate of taper on the base. It is a very important point to appreciate the shape of blades.
The word "fumbari" means straddle or standing with power on the legs.
This buddha is "fumbari-ing". (a statue in Kamakura period)
Fumbari is very effective to make blades look steady and strong. Shortened blades have no fumbari even if it has large width at the base.
For example, tachi blades in the Kamakura period (12-13c.) have a big fumbari, so when they are shortened, the fumbari disappears and the shape looks strange with its weak looking base. Such blades still have a large width at the base but the rate of the width becoming larger toward the tang is average.
An example of an original length tachi blade.
The left shows the fumbari of the original length blade. The right is the same blade holding at a 10 cm shortened position.
It is difficult to explain the difference of feeling because it is an optical effect, but very large. You should feel it by handling a real blade.
An example of O-suriage katana blade.
It was born as long tachi blade in 14th century, then it was shortened to the length that has no original tang.
It has no fumbari, even though it still has enough width.
A large width at the base and narrow head doesn't mean it is a fumbari. Such form is just a "wide base and narrow head" or "large tapered".
Fumbari is not a matter of width, but it is a matter of the rate of taper. Fumbari is a conscious width and thickness that becomes larger at the base.