Soul Edge is the de facto antagonist in the Soul series of fighting games, namesake to the first installment, and Inferno's real body. Whereas Soul Calbur represents good and light, Soul Edge represents bad and darkness. Originally forged by human hands, at first Soul Edge was just an ordinary sword, but after being bathed in blood and hatred countless times, the sword turned into a demonic weapon and gained a wicked soul called Inferno. Those who grasp its hilt are unable to escape its curse, as its spirit invades the mind like a parasite and drives its wielder insane. As its blade is soaked in blood it grows in power, yet it manages to shine a polished red. Soul Edge is distinguished by the animate eye representing its core.
Consistently referred to as the "evil sword" throughout the series, Soul Edge has a reputation for devouring souls. The weapon is also known to be a shape-shifter – which form it takes depends on its current owner. Only those with great mental discipline can retain their will while wielding this weapon. In the games, a common trait of selecting Soul Edge as a combative weapon is that it depletes the health of the player whilst giving increased attack power or even draining an opponent's health upon contact. Either way, it is not unusual for the player to lose the battle as a result of wielding the weapon, regardless of the opponent landing the finishing blow, and thereby living up to its in-game legend of "consuming" its wielder.
The second known bearer of Soul Edge was Zasalamel, during one of his many lifetimes. Trying to break the curse of his eternal reincarnations, Zasalamel obtained the cursed blade, but instead, his soul was possessed by the evil will of the sword, and he turned into the host of the blade until the end of that life. After that, records cease until several hundred years later.
During the 16th century, Soul Edge mysteriously reappeared in a secret antique auction, though it is unknown why it now existed as two blades instead of one. The swords were obtained by an English curio dealer, whose ship was attacked by the dreaded pirate Cervantes de Leon. Possessed by the will of the wicked swords, Cervantes slew the crew of the ship and then slaughtered the population of a Spanish port-town, where he stayed the next twenty-five years, waiting of the birth of the "Child of the Cursed Sword". But then a holy warrior sent by Hephaestus, Sophitia Alexandra, confronted him and was able to destroy the smaller of the two blades. About to kill her, Cervantes was stopped and killed by a demon huntress named Taki.
It was at that point when Siegfried Schtauffen found the object he had been seeking. When he tried to take the blade lying beside the dead Cervantes, Inferno (called "Soul Edge" in Soul Blade), in an attempt to restore itself, flowed into the corpse and fought Siegfried for the possession of the evil sword. Siegfried won the battle, and when he grasped the hilt of Soul Edge, he was unable to control its power, and released the Evil Seed on the world. Siegfried was further corrupted until he no longer had control over his own body, assuming the role of Nightmare. In the penultimate events of Soulcalibur, he was defeated by Xianghua after her treasured Krita-Yuga weapon revealed itself to be Soul Calibur. Xianghua then used Soulcalibur to shatter Soul Edge. However, traces of Soul Edge were still present in Siegfried's body, and he eventually donned the azure armor again.
After succeeding in restoring much of the weakened sword's power, Nightmare was challenged by a swordsman searching for the legendary blade, Raphael Sorel. Nightmare stood victorious, but with his last breath, Raphael made a desperate attack and managed to strike his sword into the very center of the cursed blade. Screaming in agony, Nightmare fell back, and within his mind, Siegfried reawoke. After a fierce mental struggle, Siegfried regained his sanity. Shining from the core of Soul Edge, the holy sword Soul Calibur appeared to him, released from its entrapment within the evil blade. Taking Soulcalibur, Siegfried drove it into the cursed blade, piercing the eye and silencing the power of Soul Edge. However, it was not enough to destroy the cursed sword.
Inferno, thrust out of Soul Edge by Soulcalibur, transferred itself into the remnants of Nightmare's armor, but could not manipulate the bodiless husk. It was then when Zasalamel appeared and agreed to help Inferno if it assisted him in finding the two swords of legends, before using his ancient powers to bind Inferno to the armor. At this moment, the evil spirit of Soul Edge became the new Azure Knight. Born from the memory of its old shape, the Phantom Soul Edge is dwarfed by the real cursed sword, but as Nightmare once again began his quest to search for his missing form, this weapon began to grow stronger. The real Soul Edge, silent with its counterpart Soulcalibur, was in the possession of Siegfried Schtauffen, who sought a way to seal the evil sword forever.
Though Soul Edge's power was vastly diminished, there were still many of its fragments scattered throughout the world, expanding Soul Edge's influence far beyond the sword itself. Cervantes de Leon carried another version of the cursed sword, born from fusing several fragments together, as did Taki with one of her blades. Even though the sword was sealed, its fragments still emitted the evil energies of the cursed blade.
Nightmare and Siegfried eventually meet in Lost Cathedral, and Soul Embrace is finally broken. The two knights clash, sending a shockwave that rips both their bodies apart, and levels the Cathedral. Soul Edge and Nightmare fell into a warped dimension, but even then, Soul Edge sought power. Because Nightmare had been given a body by the hatred and evil that dwelled there, the sword and body ended up at Ostrheinsburg when they fell out of the void. Soul Edge stretched its evil roots into the azure armor. The shockwave emitted at the cathedral had spread an evil energy that had made all of the sword's shards active, now Soul Edge called out to them and they returned, both small and great. These included the being Charade and Soul Edge's female half that was being wielded by Cervantes. These pieces had been scattered by Evil Seed, but now they were being called home. The sword drank it all in, and, for the first time in decades, was mostly whole again. But it was not satisfied, and the sword continued to stretch into Nightmare. Now, the azure knight's body, which had been formed from the lingering hatred and tormented ghost, truly became Inferno.
Finally, drawn to the sword like it was a pulsating beacon, the sword's servants began to gather at Ostrheinsburg. The evil armor was no longer enough to contain the evil power, and so the power and mind of Soul Edge sank its roots into Earth itself, and Ostrheinsburg became a cursed city, a vessel that would consume souls to further strengthen the sword. Now the sword sits and waits for the final moment when it can clash with Soul Calibur again.
Soul Edge (Cocoon) is a weaker state of Soul Edge. It has weird looking claws that extend out of the hilt area. Siegfried Schtauffen wielded this weapon in Soulcalibur II in his two player costume, and it reappeared in Soulcalibur III as an extra weapon.
A weapon that first appeared as the two player version of Soul Edge in Soulcalibur III, just like Soul Edge (Male) did in Soulcalibur II. Siegfried Schtauffen, Nightmare and Iska Farkas use the sword in Soulcalibur Legends, where it is referred to as Soul Edge Ω.
It is the so called, "complete form of the sword", and it has been redesigned three times in the series. In Soulcalibur II, when wielded by Nightmare, it looks like a reddened version of the original male version, except with teeth. In Soulcalibur III, it lacks its eye, and is a brown sword with horns and teeth. This version is used by Night Terror and later appears as Nightmare's player two weapon in Soulcalibur IV.
A long sword version of Soul Edge that is smaller than the male version. It was originally shattered by Sophitia, but was reformed and used by Cervantes until Soulcalibur IV, when it was fused into the male sword creating the complete form.
A larger version of the male blade that was most likely Soul Edge's state at the end of Soulcalibur II. It was formed after the several fragments were merged into the male sword.
The smallest and weakest looking version of Soul Edge, it is simply an all black sword with blood red stripes that has only a passing resemblance to the male sword.
The most recognizable and common version of Soul Edge, it is wielded by Nightmare in Soulcalibur and Soulcalibur II. In the end, it and the female half fused together to produce the complete sword.
Soul Edge (Phantom) is the weapon Nightmare wields in Soulcalibur III, which is formed by Nightmare when Zasalamel gives him power again. It's a materialization of Nightmare's memories of the original Soul Edge, created from his own body. It has the ability to consume souls, but other than that is just a weaker version of the true Soul Edge. It is created in a similar way to how Charade and Inferno create their own weapons from their bodies.
A version seen as an extra weapon used by Nightmare as an extra weapon in Soulcalibur IV. It is seen being used by Algol's son in the intro movie of the same game, as well as in the forth stage of Algol's story mode. Other than that, nothing else is known about it, though it has a passing resemblance to the form of Soul Edge seen in Charade's ending movie in Soulcalibur II, which is formed when Charade fuses with the sword.
The absolute, final version of Soul Edge and its strongest form in history, this form is Soul Edge's zenith of power, and Nightmare's ultimate weapon in Soulcalibur IV.