Just as it's titled, it's a key that can unlock Chaos's memory from his traic past. All he has to do is put the key into the keylock on his head. For a long time he refused to unlock his memory until just recently when he and Mantaro (as the Muscle Brothers Noveau) were fighting the 20 Million Powers. after having his Great Mask damaged further, he decided to finally use the key. The effects have yet to be revealed.