Sacred Power of the Spirits

The Sacred Power of the Spirits is a powerful energy source that dwells inside Princess Zelda in The Legend of Zelda: Spirit Tracks. The exact origin and potential of this power are unknown but it is stated by Anjean to exist only in the body of a member of the Royal Family of Hyrule and by Byrne to be the power of the Spirits of Good.

Story
Near the start of the game Chancellor Cole and Byrne attack and steal Princess Zelda's body planning to use it as a vessel for the Demon King Malladus and to augment the powerful Demon. When Link travels to the Tower of Spirits with Zelda's soul the guardian Lokomo of the tower, Anjean explains that the power is located in members of the Royal Family of Hyrule. Anjean tells them that if Malladus is revived into Zelda's body his power would over shadow the power of the Spirits of Good and it would be impossible to seal him away again. After successfully restoring the Tower of Spirits Link and Zelda try to stop Malladus' resurrection but arrive too late. Malladus however can not instantly use the Sacred Power for unexplained reasons and flees with Cole on the Demon Train after injuring Byrne because he once served the Spirits of Good. Link and Zelda confront Cole and Malladus in the Dark Realm where they banish him from Zelda's body using the Bow of Light. When Zelda tries to reclaim her body she is unable due to the linger effects of the Light Arrow. She then asks for the blessing of her ancestor Tetra and uses the Sacred Power to renter her body. Now left without a suitable vessel Malladus consumes Cole and transforms his body. Malladus appears to have full control of the new body but says his spirit is slipping from it and could not use it for long. Malladus then reveals he still posses enough power to destroy the world even without the Sacred Power. Zelda then uses the Sacred Power combined with the Spirit Flute to reveal a weak spot on Malladus. Together Zelda and Link use the Bow of Light and Lokomo Sword to destroy Malladus for good.