Kai's return to the surface was marked by a silence that was now familiar, a quiet that seemed to envelop the world above as it did the world below. The stone from the whale graveyard pulsed in his hand, its rhythm syncing with the beat of his heart.

As he sailed back through the foggy veil that separated the living from the memories of the dead, Kai felt the weight of his ancestors' eyes upon him. He was the bearer of a legacy that stretched back through generations, a legacy that was now his to redefine.

The stone's glow illuminated the cabin of the boat, casting shadows that danced like the spirits of the whales that once filled these waters. With each vision that the stone imparted, Kai's resolve grew stronger. He saw the interconnectedness of all life, the intricate web that the whales had once woven with their songs.

The memories were not just images; they were emotions, experiences, a shared consciousness that transcended individual existence. Kai felt the joy of the whales as they navigated the boundless seas, the sorrow of their loss, and the hope that still lingered in the ocean's depths.

He understood now that the whales were more than creatures of the sea; they were its custodians, its voice, and its memory keepers. Their songs were not just melodies; they were the language of the water, a language that spoke of balance, harmony, and life.

The stone revealed to Kai the forgotten prophecy in its entirety. It was a call to action, a plea for humanity to awaken from its slumber and listen to the wisdom of the ancients. The last guardian's song was a key, but it was Kai's voice that would have to carry its message.

As the first light of dawn broke, Kai reached the shores of his home. The village that had once mocked his quest now looked upon him with a mixture of awe and fear. In his hand, he held not just a stone, but the future of the ocean and all who depended on it.

With the memory keepers' stone as his guide, Kai set out to fulfill the prophecy. He would find the last guardian, amplify its song, and restore the ocean's health. The path would be fraught with challenges, but the memory of the whales, their legacy, and their trust in him fueled his determination.

The ocean had chosen its champion, and Kai would not fail.