The essential story of the Merkiri and the Merkyo is this:
The Merkiri always lived in the north. Their fishier bodies made the waters easier to handle. The Merkyo, from the south, more human in nature, were more warm-blooded, and found the southern waters easier to handle. The two species were cousins, however, living together peacefully.
However, the shark-tails grew angry with their idyllic lives. By nature, shark-tails were predators, like the sharks themselves. So they declared war on the merkiri. The Merkiri fought back, but they were not warriors. Many of them fell in battle, becoming Ghost Swimmers. These Ghost Swimmers were their most powerful elders, or those of them with the most desire to live on. They used their power to seal away the Merkiri children, some teenagers, and even the occasional unborn in unbreakable orbs. The strongest of the adults were able to survive, and flee to the south.
The Merkyo were ready. With their more humanoid upper bodies came more flexibility. They were able to lay traps that the shark-tails could not defeat. And though the most powerful of the sorcerers among the merkiri had fallen, they were still able to use their strong wills, and quick wits.
Eventually the shark-tails were driven back, but at a terrible cost to the Merkiri and Merkyo.
The Merkiri had been able to save many of their children, but the merkyo were not sorcerers. Very few of their children survived. Their race, once proud and beautiful, was almost gone.
It was the merkiri who found their orbs first. Eventually, as they found those they called 'Guardians', they were released by three of the most powerful remaining Merkiri sorceresses. Starr, Tiamat, and Night Water.
One day, however, a group of four were out exploring the waters, and came upon a beautiful orb. It was a Merkyo orb.
The four (Aqua, Evenstar, Nuria, and Malaike) didn't know what to do. Should they tell their cousins, and raise their hope? Or would they keep the orb safe from the vengeful remnants of the shark-tails, and return the orb to their cousins when it was safetly hatched?
In addition, they had found male orbs- where many males had died, and very few were believed to have survived. It was a cause for celebration, as one of the orbs was Julian, Aqua and Evenstar's own son.
Eventually the Merkyo founded a city near where the southern and nothern waters mixed. It was far enough north that the merkiri found it comfortable as well, and the mixing started. Still, the four kept their orb a secret, and have hunted for more.
The day is coming soon when the orbs will hatch, and the two races will begin to rebuild their lives. But for now, the safety of both their races lies in the continued secret that their future has been refound.