100 people from various countries were captured and enslaved. They were brought to an island called Wuhu Island and forced to play minigames. They were then put into 5 groups called Difficultys. Some families were split up, sadly.
You see, I suspect that all of the miis had common ancestors.
That over time, Wuhu was once nothing but an empty island, but over time it grew and changed as the older miis, wanted to leave an impact on the island.