Soul Edge

The Soul Edge (ソウルエッジ) is one of the two titular weapons of the Soul series video games alongside Soul Calibur. The weapon was briefly mentioned by Taki during the events of Metroid: Kamen Rider Generations Vol. 3: Fates Intertwined before making its appearance in Taki Gaiden: The Kunoichi Who Leapt Through Time.

Overview
Soul Edge is an evil sentient weapon that has the reputation of devouring souls. It is said that it a demonic being called Inferno lays dormant within the cursed sword. 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. Its blade soaks in blood and in power, and it remains a polished red. Soul Edge is distinguished by its animate eye. The weapon is also known to be a shape-shifter – which form it takes depends on its current owner (i.e., a pair of two swords for Cervantes and a zweihander for Nightmare, respectively).

Soul Edge's curse is called "malfestation", and is inflicted not only upon those who wield the sword itself, but those who come into contact with its shards. Normally, the Evil Seed transforms the person infected into a demonic monster and feeds off the host's inner sinful deeds of bloodlust, controlling and manipulating their actions, and forcing the user to take the souls of whom they defeat in battle.

In both timelines of the Soulcalibur universe, Soul Edge was first wielded by Cervantes de Leon; taking form of a pair of two (long and short) swords, but he lost the weapons after he was defeated by Sophitia Alexandra and Taki. Following that, Siegfried Schtauffen stumbles into the other pair of the cursed sword, and the sword itself bonded to Siegfried, transforming him into the Azure Knight, Nightmare who would then unleash the Evil Seed, a manifestation of the sword's evil energy that caused disastrous negative effects.

Physical Sword

 * Cervantes de Leon (formerly)
 * Nightmare (current)

Shards of the Sword

 * Taki (via Mekki-Maru)