Soul Edge (Complete)

From the Soulcalibur Wiki

The evil sword Soul Edge, after recovering all of its fragments and becoming whole once more. Even after almost covering the entire world in darkness, it is safe to assume that it has not come close to reaching the limits of its terrible power. At this point, it is not certain whether even Soul Calibur could stand against it. It can only be described as ultimate.

The complete form of the sword has been redesigned three times in the series. In Soulcalibur II, when wielded by Nightmare, it still holds the vague shape of a great sword, but appears to be made entirely out of organic material, with teeth, flesh and an abundance of eyes covering its surface, making it the most grotesque version thus far in the series. In Soulcalibur III, it lacks the 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. In Soulcalibur IV, a completely new version of the sword, itself, is created for the game, and it is used by Nightmare as his primary weapon, and looks more like a traditional sword than Soul Edge had in some time.

In addition, every single character in Soulcalibur II, not just Nightmare, had an unlockable "Soul Edge (Complete)" weapon, each of which took the form of that character's preferred weapon (a staff for Kilik, a pair of katars for Voldo, a great axe for Astaroth, etc.) made entirely out of organic material, with teeth and eyes being a common feature. This was interesting because the dark sword was usable by every character, even the pure-hearted such as Talim, and those who had dedicated themselves to the sword's destruction, such as Xianghua or Sophitia. This even counted for the guest characters; despite being considered as pure-hearted a character as can be found, Link could wield Soul Edge in the form of a sword and shield.