Opal City consists of 9 wolf-made islands with an island with a former Moonstone family king on the smallest island.
The kingdom came into existence when a moonstone family ancestor blended the 8 other powers of the other kingdoms into 1, and created the first island.
The way the city was created other people of other packs lived here as well but with passive aggressive tones and hostility between each other as they could not get along. Until recently the Unity pack wasn't doing it's job to unite each other, it wasn't until Artemis and his fellow princes showed that people of different kingdoms can get along in perfect harmony. As for many years the Kingdom was divided with the Moonstone family not doing much to change it which was a reason Artemis sought to change things.

Note- The Moonstone wildcard power only appears more easily in males than the females of the family and works like the Wildcard power from the persona Games. The only difference Between the two is the Moonstone power can only mimic it so well not a perfect magic copy of that ability or power.