Soul Edge is one of two legendary swords central to the plot of the Soulcalibur series. Soul Edge is often compared to other epically huge blades, and while the lore behind this giant blade has changed with Soulcalibur VI's reboot, the original timeline still holds plenty of key information about Soul Edge.
Soulcalibur stands out from other early generation fighting games such as Killer Instinct and Mortal Kombat due to how much care Project Soul puts into the games' lore. It wouldn't be until Mortal Kombat: Deception redefined the importance of lore in fighting games that other fighting games started to follow Soulcalibur's example.
Soul Edge's origin involves a man by the name of Algol. The Hero-King Algol was able to overpower the evil blade's intelligence and wield it to bring peace and prosperity to the world. However, his son would fall victim to Soul Edge's manipulation, resulting in Algol killing his son. Algol would then give his own life to create a divine counterpart to Soul Edge to protect others from falling victim to its corruption. This counterpart would be called Soul Calibur.
Soul Edge would continue to use its corrupting nature to jump between hosts. This corruption is known as malfestation and spreads through both Soul Edge and its shards. Eventually, this malfestation would find its most well-known host, Siegfried Schtauffen. Siegfried would search for the blade, eventually finding it on the body of the dread pirate Cervantes de Leon, who had been killed by a ninja known as Taki and a champion of the Greek gods known as Sophitia Alexandra.
The malfestation would corrupt Siegfried until he would lose control of his own body and become the Azure Knight, Nightmare. Nightmare has taken on several forms across multiple hosts, though he'd remain in the body of Siegfried for the longest. Whilst infesting Siegfried's body, Soul Edge would eventually grow powerful enough to manifest itself without a host.
Soul Edge would be split from Siegfried after a fatal duel with the French noble Raphael Sorel. Siegfried's mind would fight against the cursed blade, causing Nightmare to freeze in place. Raphael would take this opportunity to strike Soul Edge in its eye, freeing Siegfried from its control. Siegfried would then pull Soul Calibur from within Soul Edge and attempt to destroy the cursed blade.
This, however, would prove to be ineffective. Though the sword part of Soul Edge would be destroyed, the corrupt soul inside would live on. Known as Inferno, the corrupt soul would possess Siegfried's discarded armor that he wore as Nightmare. With the help of a sage known as Zasalamel, Inferno would become powerful enough to control the armor independently.
There was a drawback to Soul Edge no longer requiring a host, as the blade's evil energy began to grow too powerful for the lifeless armor to withstand. This led to Soul Edge corrupting the very Earth itself, turning the city of Ostrheinsburg into a cursed land that would absorb the souls of those killed there. By this point, Soul Edge had managed to corrupt many followers through both the sword's presence and the shards of its original blade. These followers would seek both a new host for Soul Edge and souls to feed to the blade.
Soul Edge would wait for an inevitable final clash with Soul Calibur and Siegfried. This fight would occur and lead to both Soul Edge's and Nightmare's destruction. Siegfried, wielding Soul Calibur, would shatter Soul Edge into fragments. These fragments would spread themselves across both space and time. However, much like before, Soul Edge would not truly be defeated.
Those who Soul Edge had corrupted would gather the shards of the cursed blade and reconstruct it. However, the sword was weakened once again and would require a new host. The identity of this final host is only ever canonically referred to as Graf Dumas. However, there's a fan-theory with a wide amount of evidence that the true new host of Soul Edge was Raphael Sorel.
After Soul Edge's first destruction, Raphael would become corrupted by the wounds he had been dealt during his battle with Nightmare. The sword drove Raphael to madness, leading to his obsession with finding Soul Calibur, as he believed it to simply be a stronger version of Soul Edge. Raphael would wait for many, many years for Soul Calibur to appear.
At this point, the fan theory uses evidence from Soulcalibur V's artbook to state that Raphael's malfestation eventually killed him, leading to his body being found by Soul Edge's followers. He would be presented as the new host for Soul Edge, which would wipe his memories to hold its control over him. Raphael would become Graf Dumas and the new Nightmare, though he would eventually be freed from the sword's corruption.
This is where the original timeline's lore for Soul Edge ends. The rebooted timeline in Soulcalibur VI is outlined until Siegfried's corruption into Nightmare, though most of Soul Edge's original lore is intact. The blade is still capable of corrupting people, shards of Soul Edge are still scattered throughout the world and Soul Edge can still take on multiple hosts.
Throughout six games and a timeline reboot, the lore of Soul Edge paints the blade as a truly evil entity. Soul Edge serves as the main antagonist of most of the Soulcalibur franchise as well as the MacGuffin that multiple characters have their plots and arcade mode stories framed around. Soul Edge is one of the most iconic and terrifying swords in video game history, with plenty of haunting lore to back up that legend.