Kai's boat glided through the water, a silent vessel amidst a sea of memories. The song had led him to a place beyond the realms of the living—a graveyard of giants, where the bones of whales lay scattered across the ocean floor like the ruins of a forgotten civilization.

The water here was colder, its currents carrying the whispers of a thousand tales. Kai felt the presence of the ancients, their spirits lingering in the hollows of their earthly remains. The melody that had guided him this far now resonated with a somber tone, a dirge for the departed.

As he maneuvered through the skeletal remains, Kai's eyes were drawn to the intricate patterns etched into the bones by time and tide. They told stories of epic migrations, of battles fought, and of the deep, enduring connections these creatures had shared with each other and the ocean that was their home.

The song grew louder, more insistent, as if the graveyard itself was singing. Kai followed the sound until he reached the heart of this underwater mausoleum. There, nestled within the skull of a whale larger than any he had ever imagined, was a stone pulsating with a life force of its own.

It was not just a stone; it was the heart of the ocean, a memory keeper of all that had been lost. As Kai reached out to touch it, the stone's glow intensified, and a rush of visions flooded his mind.

He saw the whales in their prime, their bodies slicing through the water with grace and power. He heard their songs, a complex tapestry of sounds that wove the fabric of the sea's very essence. And he felt their pain, their sorrow as their numbers dwindled, their songs silenced by the greed of man.

The visions shifted, and Kai was shown the prophecy—a warning of what was to come if the balance was not restored. The last guardian's song was a key, a beacon that could awaken the memory of the ocean and bring back the harmony that had been lost.

Kai emerged from the vision with a newfound purpose. He was no longer just a descendant of whalers; he was a guardian of the ocean's past and a herald of its potential future. The graveyard was not a place of death, but a cradle of life waiting to be reborn.

With the memory keeper's stone in his possession, Kai set his course back to the surface. The song of the ancients had become his own, a melody that he would carry to the ends of the earth if it meant the salvation of the seas.