Power of waking

The power of waking (眠りし心を解放する力) is an ability introduced in Kingdom Hearts 3D: Dream Drop Distance, and is a key plot element in Kingdom Hearts III. It is described by Yen Sid as "the power to free a heart from its sleep".

Only Riku, King Mickey, and Sora are known to posses the power of waking.

Abilities
True to its name, the power of waking is able to awaken a sleeping heart.

The power of waking can also use hearts as an intermediary to travel to certain worlds. It can additionally be used to reach the Realm of Darkness, and is one of few ways to do so outside of using a Corridor of Darkness, or a world becoming unstable.

Unintended uses and consequences
However, the power of waking has unintended uses - since the states of sleep and death are connected, it is possible to use the power to restore recently-deceased hearts. Furthermore, the ability to use hearts to reach worlds can be reversed, instead using worlds to reach hearts.

Abusing the power of waking in these ways is a "nature taboo", and incurs a high price for the offender - their power of waking will be revoked, as well as some of their other abilities, and they will vanish from the world where they originate. As a result, the offender will be unable to return to their original world without outside assistance.

Kingdom Hearts 3D: Dream Drop Distance
Sora and Riku take a Mark of Mastery exam to not only be named Keyblade Masters, but also obtain the power of waking by awakening the Sleeping Worlds. However, Sora loses this power when Xehanort corrupts his heart with darkness. After passing the exam and defeating Xehanort, Riku uses the power of waking to dive into Sora's heart; there, he defeats the Armored Ventus Nightmare and awakens Sora by answering three questions in a vision of the Destiny Islands.<!--

the purpose of sora and riku's exam is to gain the power of waking, and riku uses it to wake Sora:

Yen Sid: If we are ever to strike down Xehanort, we need the individuals King Mickey spoke of in his letter. We must lead them out of sorrow and slumber, and back to our world. To do so, seven Sleeping Keyholes must be found and unlocked, and a great power retrieved. As you know, every world is walled off from the next, preventing travel between them. In the past, you could bridge these gaps because the walls were broken, or because you could open special Lanes with your Keyblades. But your new goals, the "Sleeping Keyholes," are harder to reach. You'll recall, in your first journey, that you brought many worlds back from the darkness--but some never returned completely. They still sleep, cut off from all outside channels. Not even the Heartless can enter.

Yen Sid: You must understand, this examination is in no way how the Mark of Mastery is usually found. However, in light of what they must do next... it was a necessity. If Sora and Riku complete their test, by finding the seven doors corresponding to the seven pure lights, they will return home with a new power.

Yen Sid: In your Mark of Mastery exam, you were to unlock seven Sleeping Keyholes. By doing so, you would awaken those worlds from their prison of slumber, and also acquire the power to free a heart from its sleep. Riku, you unlocked those Keyholes within Sora's dreams. Therefore, it stands to reason that you now have the power to awaken Sora's heart. Mickey: You want him to dive back into Sora's sleep? But Master, Sora's heart is down in the darkest abyss. If Riku's not careful, he might just get trapped down there with him. No... I'll go instead. --note: "power to free a heart from its sleep" probably "power of waking" in original JP script

Yen Sid: More than anything, I am grateful to have you both back from Xehanort's deception unharmed. And I am grateful to Lea, whose spontaneous actions turned the tides. I am also deeply sorry, for failing to percieve the danger and throwing you headlong into a perilous test. This experience has revealed many hidden truths, and we must gird ourselves for the great clash with darkness that lies before us. I believe we need a new Keyblade Master, one with a new kind of power. Sora and Riku, you both deserve the honor. However, one of you braved the realm of sleep again to unlock the final Keyhole and save a friend. Riku, I name you our new true Keyblade Master.

Ansem the Wise: Yes. A clue, I hope, to finding yourselves or your lost friends in your hour of need. The heart has always been quick to grow. Each exposure to light, to the natural world, to other people, shapes this most malleable part inside of us. Nobodies are not different from us in that manner. Sora was the only one able to return to his human form without destroying his Nobody. That is a statement to the love in his heart for other people, and the bonds that tie them together. Perhaps...he has the power to bring back the hearts and existences of those connected to him-- to recreate people we thought were lost to us forever. Our most precious treasures--even an empty puppet--the trees of the forest, and the petals on the wind--there are hearts around us everywhere we look. And it does not take superhuman powers to see them. Surely we remember as children the way our hearts made everything seem so shiny, and perfect. Sora has a heart like that--uncorrupted, willing to see the good before the bad. When he sees the heart in something, it then becomes real. When a connection seems broken, he may have the power to mend it. He has touched countless hearts, he has accepted them, and he has saved them. And some of those hearts have never left him--whether they fell into darkness or were trapped there--whether they sleep in the darkness of Sora's heart, or were welcomed into its warmth--they can be saved. All Sora needs to do is be himself and follow wherever it is that his heart takes him. It is the best and the only way. The rest is in there.

Ansem the Wise: You see, by defeating the Nightmare imprisoning Sora, you freed him.

Riku: You mean...the Sora wrapped in that black phantom?

Ansem the Wise: Then, you came here, and you were questioned by three young people. That was the final key to awaken him.-->

Kingdom Hearts III
Sora travels through the worlds in an attempt to regain the power of waking. Upon facing Vanitas at The Land of Departure, Sora realizes with Ventus's help that the power of waking is still sleeping within him. He then uses the power of waking to free Ventus's heart from within his own and awaken him from his eleven-year coma.

After rebuilding his body in The Final World, Sora uses the power of waking to travel between facsimiles of the worlds and track down his friends' hearts, in an attempt to save them from the Lich. He succeeds and sends them back in time to their arrival at the Keyblade Graveyard. As a result, Sora creates a tear in the fabric of time known as a singularity and changes history so that Sora's friends are saved by the Lingering Will.

Kingdom Hearts III Re Mind
After the final battle with Xehanort, Sora travels back in time to before his arrival at Scala ad Caelum to save Kairi's heart. He succeeds, but having repeatedly used the power of waking to restore hearts that have been erased from existence, Sora vanishes into another world.

Kingdom Hearts Melody of Memory
After a year of searching for Sora after he disappeared, the Fairy Godmother takes Riku and Kairi to the Final World, where they meet the Nameless Star. The Nameless Star opens a to the world of Quadratum, and Riku uses the power of waking to travel through it.