Heart of Kandrakar

The Heart of Kandrakar (or Heart of Candracar) is a magical pendant that bestowed to the leader of the Guardians of the Veil, and enables the Guardians to transform into their superhero alter egos by channeling the power of the Aurameres into them. Although the Guardians have some power without the Heart, their strength is greatly increased by it. Without it, the Guardians' powers would be drawn from their life force instead of the Aurameres.

the Heart is a unique magical jewel that merges with its holder's body when it is not in use, and retains a shade of them when it is passed on to the next holder.

the Heart remains distinct from its owner, and each world had a Heart of its own. Some of which are jewels like the Heart of Kandrakar, and others of which are people with tremendous magical power.

It's revealed that Elyon is the Heart of Meridian, and Lillian Hale is the Heart of Earth. It is also revealed that the holder of one Heart can merge it with another world's Heart, but only if that Heart is given willingly. However, the Hearts of each world cannot be taken by force. They must be given willingly, which is why Nerissa had to resort to trickery to acquire Elyon's powers instead of direct confrontation or stealing it from her. This means that the Heart of Kandrakar is literally the "Heart" of Kandrakar, and possibly its central power source, or perhaps vice versa. In the comic book, the Heart is the symbol of Kandrakar, which explains the reason the Oracle's head is marked with its symbol. Also, even the Oracle does not have the power to demand the Keeper hand it over, and the Keeper must decide to return it, which is the reason why Endarno does not simply use his powers as the new Oracle to take the Heart from Will, which would enable him to succeed in his evil scheme and greatly weaken the Guardians.

Origins
there were once four dragons: the Long Dragon, the Yellow Dragon, the Pearl Dragon and the Black Dragon. The dragons were compassionate and wise and were very upset when they saw that the world below was having a long drought. They appealed to the cruel and vain Jade Emperor but he refused. Taking matters into their own hands, they scooped water into their mouths and rained it onto the land below, saving the people.

This infuriated the Jade Emperor and he ordered that the four dragons be locked away forever in four mountains. A kind and wise nymph named Xin Jing (Chinese: 心晶), meaning Heart of Crystal in Chinese, felt that this was unjust and confronted the Emperor. Though unable to undo his spell, she still wished for the dragon's noble deeds to be remembered. She absorbed the Dragon's essence and became a dragon herself, flying away. The four dragons became the four rivers of China. After, all that remained to remember Xin Jing was a crystal pendant that contained the Dragon's essences plus her own. The crystal was named the Heart of Kandrakar.

in the different animated version, there once was a kingdom that was suffering from a prolonged drought.[3] Feeling pity for the people of the kingdom, the Jade Emperor's four dragons came together and used their magical abilities to bring rain to the land. However, in doing so they enraged the Emperor himself.Angered that they had acted without his permission, the Emperor ordered that the dragons be confined in the hearts of four mountains. The Emperor's daughter, however, realized that the dragons were right in helping the people. She argued with her father and when he refused to reverse his decision she freed the dragons herself. After being freed from their mountain prisons, the dragons became one with the Emperor's daughter, and she left. All that remained of her was the Heart of Kandrakar.

The Heart is shown to have a strong bond with its keeper, leaving a spark within them and always coming back to them. It has also been revealed that it is not the Keeper who chooses the Heart, but the Heart that chooses the Keeper.