Keyblade of Heart
The Keyblade of People’s Hearts was made by Xehanort's Heartless with six of the seven Princesses of Heart's Hearts. Though, it was incomplete without the seventh. It could be considered "artificial", due to its synthetic construction from hearts. Because of this, the weapon is not cosidered a true Keyblade. It also lacks a keychain, possibly because it was artificial, or because it lacked the heart of the seventh princess.
This Keyblade has the power to "unlock" the Darkness in people's Hearts. In Hollow Bastion, Riku, while under the control of Xehanort's Heartless, used it to "unlock" Maleficent's heart. This floods the witch's heart with Darkness, transforming her into a large Dragon. There also seems to be a side-effect to the Keyblade's power, as after Sora defeated the dragon, the Darkness completely overtook Maleficent, causing her to wither away.
Near the Final Keyhole, Xehanort's Heartless told Sora about Kairi's heart residing within him and then proceeded to attack and release Kairi's heart from Sora. However, Sora defeated his possessed friend and then turned the Dark Keyblade onto himself to unlock Kairi's heart. The stab from the Dark Keyblade turned Sora into a Shadow. This created his Nobody, Roxas, as well as Naminé, who was born from both Sora and Kairi.
The Dark Keyblade then vanished, turning back into the other six princesses' hearts. To this date, it hasn't been seen in any other games in the series.
