Wasn't Oblivion the dark Keyblade Riku/Ansem used to open hearts? As fas I remember, Sora thrusted the dark Keyblade in his own heart to free all the Princesses of Hearts, and the Oblivion was destroyed. However, when you return to Hollow Bastion, you can still get the Oblivion. Doesn't that mean that if you equip Sora with Oblivion, he's using the dark Keyblade which is opening people's hearts? Or is Oblivion just a keychain that works in both light and dark Keyblades?