At the dawn of the 30th Century, dolphins and humans had been together in a cross-species society for 500 years. Together, they had set out to explore space, offering peace and friendship to all who would welcome it. But space had its dangers; a violent species known as the Foe decided to conquer Earth. However, the dolphins and humans drove them to the brink of defeat, and so the Foe sought vengeance on Earth. The few caretaker dolphins who had been left behind on Earth were not entirely defenseless; they were protected by their creation called the Guardian—a gigantic, sentient being made of a crystalline substance which projected a forcefield over the entire planet. Undeterred, the Foe made suicide attacks on the field, searching for a weak point.

In the past an aggressive alien race called The Foe had engaged in armed conflict with the inhabitants of Earth. Back then, they were defeated by the combined force of humans and dolphins working together to repel the invasion. Now, a new war is raging between the two. The Foe have a new objective this time, the destruction of the Guardian, a giant crystal that is the nucleus of the Earth's defence system. The Guardian protects the planet from exterior attacks via a powerful forcefield. However, the Foe somehow find a way to penetrate the barrier and destroy half the Guardian with it. One of the Guardian's shards makes contact with Ecco and informs him that only he can save the planet from destruction.