The shape of the earliest Japanese swords, according to modern archaeological experts, came from the heavenly sword-work during the Heian period. The master sword-smith of the period was the famous Taishou Xiaowu Maru.
Since then, after the Kamakura era, the Northern and Southern Dynasties era, the Muromachi era, the Antu Momo era, and the Edo era, the shape of the Japanese sword gradually formed into the style seen today. Also during the Antu Momoyama and the Edo periods, the length of the blade was regulated.
Due to the changes in its form and use in wars, the shape of the Japanese sword has gradually evolved. One of the most significant changes was the transfer of the Jingdu, which first advanced from the stem reverse and the waist reverse cut.
Many different styles arose and these were all safe. The ancient sword-smiths of the Northern and Southern Dynasties practiced the treatment of grinding and even used this to shorten the length of the sword.
In the Edo period, the main application of Japanese swords was no longer in the battlefield, so they were transformed into an expression of high quality swordsmanship. As a result, the Japanese swords in the Edo period were much weaker than the swords of the previous era. 
From the later periods of Heian to the Kamakura era, Japanese swords appeared in the sword-making genre known as the "Five Legends of the World", including Yamato, Bizen, Yamashiro, Aichi, and Mino as well as other famous craftsmen from all over the world. In particular, Nagunacho is preferable from the former eras.
Iron swords appeared in the middle of the Japanese Tomb Period (200-771). At that time, the most commonly used raw material was iron. As an example of this, there have been iron swords unearthed from the Inari Mountain Tomb in Saitama and the Mountain Tomb in Shimane.
The "Golden Inscription Iron Sword" unearthed from the Inari Mountain Tomb was produced in 471 AD to commemorate the merits of serving the emperor. The sword is engraved with 115 Chinese characters. Unfortunately, many swords of this era have corroded over the years.
Golden Inscription Iron Sword
Swords before the end of the Heian period were classified as ancient swords, and the shape of the sword was different from that of common Japanese swords. These swords were either straight-edged or double-edged.
Ancient swords are extremely rare and are important archaeological finds. The Japanese sword originated from the ring sword that was first produced in China. The steel forging process introduced by Mainland China and North Korea provided the origin of the Japanese iron sword forging process .
At the same time, the fern hand sword of the Ainu people in Hokkaido is a Japanese original, and its development history is as follows:
• Ancient straight-edged horizontal sword-fern
• Hand sword (end of the Yayoi period, the ancient Tomb era and the early Heian era)
• Mao pull shape fern hand sword
• Mao pull shape (Tai Dao-Tai Dao-Tai Dao, hit the ribs sword) short sword
Swords from the 7th to 8th Century
Swords from the 7th to the 8th century were relatively well preserved. These famous swords include the Bingzijiao sword, the seven-star sword in the Temple of the Four Heavens, and the gold and silver swords of Tangzhuang in Zhengcangyuan, etc.
Some people think that these swords were mostly imported from China and North Korea. Japan was deeply influenced by China during the Tang dynasty, so "Tang people”, Tangcao" and other expressions vary.
Later, for items imported from overseas, they received the name "Tang xx", but this is not specifically referring to China. Korean imported products were also called "Tang xx”. First of all, the sword of Tang Cangyuan’s Tang Dadao was thought to have come from Mainland China.
This is by no means certain, because it is unknown whether it really came from China or North Korea, and there is no conclusion to this day (of course, the likelihood that it came from China is extremely high). Also, “Tang-like” swords referred to the Japanese swords built in Japan with the style of imported products.
From this it is very clear that the Tang Dadao is not a Japanese product. Tang-like Dadao is a Japanese product. The difference between the two is very small. One of the differences is that Tang-like Dadao is curved, while Tang Dadao is typically a straight bladed weapon.
Tang Dadao is not a Japanese sword, it is in every sense a Chinese sword. The Tang-like sword is a wild sword. Because the sword is mounted, it is referred to as "Tang-like", but the blade is not straight, nor does it imitate the sword of the Tang Dynasty.
In this era, Wu (the general term for a sword from southeastern China) was considered the best because of the use of charcoal, non-sulfur and other undesirable substances as a heat source. After the reunification of the Chinese dynasty, the production of standardized equipment began to utilize sulfide.
Coal was convenient for mass production, so the standard swords used by soldiers after the Southern Song Dynasty were obviously inferior to the swords used by the Japanese Samurai. Specially made swords are not necessarily the same, and the number of famous swords may not be less than the famous ones produced by the Japanese.
However, most of the famous swords were buried with their owners due to tradition. It is almost impossible to find these passed on to the world. This is in appreciation of the ancient emperor's poems. At the same time, the large inflow of foreign forging technology caused Japan's forging levels to rise sharply.
The number of swords left in the early Heian period is quite scarce, and the raw material and technology was changed to slightly roughened iron milling, while the appearance remained stick-shaped. Learning about the changes in Japanese sword style is not always easy, when Japan created a unique scimitar this had not been fully explained.
It is generally believed that after the chaos of Chengping and Tianqing in the middle of the Heian era (around the 10th century), the straight sword gradually changed into a machete. At the same time, the production process had also been changed from flat to diamond-shaped picks.
Improvements in the manufacturing process made Japanese swords stronger and sharper. The typical style of this transition period was the "hair-pulling large sword" made from the whole body of the blade, and the "Xiaowumaru" type sword with a double-edged structure and a curved blade. The hair-pulling large sword is the most known because Fujiwara Hideo used one in the Ise Shrine.
In the later period of the Heian era, especially during the "first nine years of battle" and "the last three years of battle" periods where the samurai forces were the most active, the samurai gate forces increased, and the Japanese sword experienced great development.
For example, Boqiguo and Binqianguo, which produced high-quality iron ore, as well as Yamashiroguchi and Yamatoguchi, which are political and cultural centers, saw swordsmen of different genres emerge. At this time, Japanese swords were mainly used for decisive battles.
For Taidao, the representative works of the period are Lai Guang, who created the "Tongzi cut" of "Drinking the Boy" in Dajiangshan (the Angang system of Boqiguo, the national treasure of Japan), and the "Little Fox Maru" that the fox helped create (the Sanjo lineage of the Shancheng Kingdom was destroyed during World War II).
In addition to Angang, the Sanjo Yeozong of Yamashiro (now Kyoto), the former Yubei Gubei, etc. are considered to be the oldest works of swordsman to be inscribed with the name of the creator.
Japanese Royal Court Sword
The characteristics of the Taihei in the Heian era are:
• Andong (い お り む ね, Iorimune)
• Small cutting first
• Jing anti
• Narrow front and wide
• Beautifully shaped swords
The Japanese sword in the early Kamakura period was similar to the end of the Heian period. The establishment of the military system of the Kamakura Shogunate dramatically increased the activity of the sword industry.
The Emperor Toba even set up Yufan forging and smelting, and Yueyue called sword-smiths to forge the sword, and actively encouraged the sword to be made. Emperor Toba himself was also an excellent sword-maker, and the Japanese sword he made himself is called the "Kuyu Forge".
In the mid-Kamakura period, due to the importance of usability, the blade width was wide but the overall width was small. The head of the sword was cut first, and the style was mainly firm and hard. During this time, short sword production began to flourish.
At the end of the Kamakura era, the social unrest brought about by the two invasions of the Yuan Army and the collapse of the original political system provided a real boost for the sword-making industry.
The Japanese sword of this period is bolder than the Kamakura mid-style. They inherited and developed the characteristics of a wide blade width and small changes in overall width, and the cutting edge was longer. Short swords, tai swords and other swords all have the same characteristics during this period.
In the era of the Northern and Southern Dynasties, a lot of large swords called Da Tai Dao and Ye Taichi appeared.
After the middle of the Muromachi period, Japanese swords changed from a sword worn downwards to a sword worn upwards.
Since the transition to peace time, the demand for swords in Japan decreased, and Japanese swords have been mass-produced as trade products, so the quality of Japanese swords began to decline. The war caused by Yingren’s chaos exploded the demand for swords again. In order to meet the demand, a large number of rough and ready products appeared, which drove down the quality of Japanese swords even more.
In the Edo period, the forging industry prospered in Edo (present-day Tokyo) and Osaka and famous swordsmen appeared from everywhere. As the prosperity of the Taiping Dynasty continued, the Japanese sword began to blindly pursue beautiful blades, gradually deviating from the essence of practicality. In addition during this era, the decoration of swords such as yam, small handles, eyes, and knots began to develop.
After the unrest at the end of the curtain, the Sui Xinzi Zhengxiu and other authorities advocated the restoration of the ancient sword forging method, and once again promoted the practical Japanese sword making method.
swords produced after this were called the “new sword”. Just as sword making began to flourish again, the Meiji Restoration began. Fighting was banned in 1873, police were banned in 1876, and scrapped swords with some others from outside the military were introduced.
Japanese swords declined rapidly as a result of all of this. In modern times it is a traditional craft, the ancient sword making method is still popular everywhere.