The dawn of a new day brought with it a sense of anticipation that rippled through the air. Kai and Dr. Nair stood on the deck of a ship, surrounded by a sea of technology and a crew united by a singular mission—to broadcast the last guardian's song across the oceans.

The underwater speakers, strategically placed in the depths, were ready to carry the melody to every corner of the blue expanse. As the first notes of the decoded song played, a hush fell over the team. The sound was pure, a clear call that pierced the water and traveled far beyond the horizon.

Kai closed his eyes, feeling the song resonate within him, a harmonious echo of the memory keepers' stone that pulsed in his pocket. The ocean responded, a gentle stirring at first, like the waking breath of a giant.

The song spread, a wave of sound that touched the hearts of all who heard it. It called to the creatures of the deep, a beacon of hope that beckoned them to return to the waters that had once been their home.

As the melody continued to play, the ocean began to awaken. Life, long dormant, stirred in the abyss. Shadows moved, forms took shape, and the silence that had reigned beneath the waves was broken by the return of its rightful inhabitants.

Whales, their forms majestic and timeless, answered the call. They breached the surface, their songs joining the broadcasted melody, a symphony of life that heralded a new beginning.

The ocean was coming back to life, its depths once again a cradle of biodiversity. The song of the last guardian, amplified by human hands, was a catalyst for change, a key that unlocked the potential for renewal.

Kai watched, tears of joy and relief mingling with the salt spray, as the sea around him transformed. The prophecy was unfolding, the balance being restored, and the ocean's song was a symphony of hope for the future.