Masamune
One of the signature qualities of Sephiroth is his sword, this is the truth behind it.
Masamune
Masamune was a famous swordsman who was first known as Goro Nyudo, who was said to have lived and worked in Sagami province during the Kmakura Era (from 185 to about 1332). He is known as the best swordsmith of Japan, aside from being a popular philosopher. He originally was apprenticed under Kunimitsu, the first famous swordsmith in Kamakura, Sagami province. Masamune worked under him and seemed to have been active from Kamakura to the early Nanbokucho period. (1333-1391)
Masamune was said to have founded the Soshu School (Soshu Kitae) tradition of swordmaking. Soshu Kitae is actually a technique where seven layers of lamination were used to make the blade. The heart of the blade is formed from softer, more malleable steel giving it exceptional flexibility. There is then a layer of slightly harder steel bonded to each side of the blades heart, giving it support. The last layers are a very hard steel bonded to the top, bottom, and both sides of the core forming the ha (cutting edge) mune (back edge) and shinogi-ji (blade flats). This form of laminar construction provided for a sword that could be sharpened to a razor edge due to the hardened steed used for the ha, but was extremely resilient to battle damage due to its softer more flexible core. Masamune's adopted son, Sadamune succeeded him as master of the Soshu tradition.
In addition, legend has it that there were "10 Disciples of Masamune," or ten swordsmiths that continued working in Masamune's Soshu tradition of sword making, and that several already well-known swordsmiths also came to study with Masamune. The Masamune Jittetsu, as these smiths were called, worked in their own tradition as well as studying the techniques of Masamune.
Regardless of whether or not this is a historical fact, the swordsmiths working at the end of the Kamakura to the Nanbokucho periods produced works with the surface texture featuring nie, a distinguishing feature of the Masamune style. Nie are areas of bright crystalline structure in the hamon (temper-line) or ji (the blade surface between the ridgeline of the blade and the hamon), resulting from the interaction of the steel during the quenching process. Masamune's style is often referred to as "the beauty of nie," putting his blades in distinct contrast with Bizen blades.
Masamune's school of swordmaking is also often characterized by the soft, flowing hamon visible on his blades. A proper polish is required for the activities in the hamon to be well visualized. (An active hamon is normally the mark of a better quality blade.)
Documented Swords
Masamune created many superb swords, and all of his surviving blades are considered national treasures in Japan. Seeing his signature on a sword is extremely rare, and there are just a few swords authenticated as his work. This body of work includes a few unsigned swords attributed to him. Their splendid craftsmanship has led to the high praise of Masamune as a master swordsmith. "Fudo Masamune," "Kyogoku Masamune," and "Daikoku Masamune" are accepted examples of his genuine works.
Masamune's works are the most frequently cited among the swords listed in the Kyoho Meibutsu Cho, a catalogue of "excellent swords" in the collections of daimyos edited during the Kyoho era (1716-1736) by Hon-ami.
Today, the name Masamune has become synonymous with "an excellent sword".
Masamune and Muramasa
It is said that Masamune had taken on an apprentice named Muramasa, who was also an excellent swordsmith despite their difference in style. There is a popular Japanese story detailing the difference in their swords.
Masamune was an old swordsmith master whose apprentice Muramasa was gaining fame each day because of the perfection of his craftsmanship and the seemingly inherint ability of his blades to deliver clean kills with every stroke.
A lord asked Muramasa one day how he made such fine blades. Muramasa said "when I complete a blade, I dip it into a stream blade first and hold it until a floating leaf comes in contact with the blade. If the leaf is sliced cleanly in two then I knew it as ready."
The noble lord was impressed greatly and started to shower praise upon Muramasa when Muramasa stopped him. He said, "my blades are fine but not as fine as my master's. I have never made a single blade that compared to Masamune's." The noble lord asked how this could be and Muramasa responded "when my master placed his blade in the stream he also waited for a leaf to float towards it. But the leaf floating directly towards the edge of my masters blades always miraculously went around the blade missing it completely. You see... my masters blades had the ablilty to protect life and preserve the order of things. Mine could only kill."
It's a peculiar dichotomy to know that Sephiroth's main choice of weapon, the Masamune, was known to save lives, while one of Cloud's weapons, the Muramasa, was only good at killing. One would normally assume that given the myths and stories regarding both swords, that Sephiroth would be wielding the muramasa and Cloud would have the masamune, instead of the other way around.
Resemblances: Inu Yasha
Both of these swords may also have some peculiar resemblance to the anime series Inu Yasha, where Inu Yasha possesses the Tessaiga, a sword that can kill a hundred demons in a single blow. His half-brother Sesshoumaru on the other hand, possesses the Tensaiga, which brings people to life rather than killing, which makes it almost useless in his perspective. Yet, Inu Yasha is the half-demon who wants to protect his friends, and Sesshoumaru only wants to grow stronger. Again, it's very interesting to know that the Tessaiga and the Tenseiga wind up in the hands of those viewers don't expect them to possess.