Corruption Key (RoTs)

The Corruption Key, also known as Master Xehanort's Keyblade or Sai-Blade (ψ-Blade), is a Linchpin Keyblade wielded by Master Xehanort and eventually his modern-day successor: Xehanort, in the Road of Twilight series.

This unique and mighty Keyblade was believed to have been the cause of the Keyblade War, when it introduced Darkness and evil desires into the Hearts of multiple Keyblade Wielders on Master Xehanort's quest to gain control of Kingdom Hearts with the χ-Blade, it was used to create the Dark Chasers organization who treat the Master-less Keyblade as though it were an object from their messiah.

Trivia

 * The Letter "ψ" is one of the only Greek Letters that didn't stem from a Phoenician alphabet root.