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The Key of Memory and Destruction is an artifical Keyblade in Kingdom Hearts AF wielded by Aros, the insane replica of Sora.
The keyblade looks just like Sora's Kingdom Key but when Aros is at full power it changes to a black colour. It allows him to absorb and trap Nobodies, giving his blade numerous powers. When he takes Namine's essence from Kairi, The Key is then granted the power to destory all hearts by erasing the person's memories on impact including being able to destroy Kingdom Hearts. Any other powers it has is generally unknown.