The Olympus Stone is an object in Olympus Coliseum from Kingdom Hearts II. It has the ability to protect people from the weakening effect of the Underworld, which, in terms of gameplay, has the ability to unlock the Drive Gauge. The Olympus Stone also is the keychain token for the Olympia, Hero's Crest, and Mark of a Hero Keyblades.
Kingdom Hearts II
The curse is first mentioned when Sora, Donald, and Goofy tried to attack Hades to get him to stop sending enemies to Hercules to fight. When Sora asks Hercules if there is a way to fight Hades, Hercules mentions the stone. When Hercules goes up to Mount Olympus to retrieve it when it was stolen. Sora later finds out that it was Demyx who had stolen the stone. The group fight Demyx's water clones to defeat him and win back the stone from him as he retreats. With the stone, Sora, Donald, and Goofy feel their strength return and are able to fight. Later, the stone helps open the Gate to a new world: Disney Castle.