Disclaimer: I don't own Fullmetal Alchemist or the idea of the Little Mermaid
The kingdom of Resembool was a very unique kingdom, unlike any ever heard of, for it was a kingdom inhabited by merpeople. It was a small kingdom, but it was very connected, everyone knew one another. There was no crime or groups, everyone and everything were equal. But above all the merpeople were a special family, the royal family, the Elrics.
The Elric family kept the piece and maintained order in the kingdom. The King was Van Hohenheim of Light. He had married Queen Trisha, who bore him two sons. The oldest son was Prince Edward, the heir to the royal throne. The youngest son was Prince Alphonse.
But one day, the peace of the kingdom was thrown out of balance with the Queen's death.
She always had a fascination with the human world, but one day she had been snagged in the tail by a harpoon when she got to close to a ship. She escaped, but infections followed her. She fought fever for a year and finally succumbed to death before the winter months.
The kingdom mourned the loss, but the King was furious with the humans. He hated them. He made it a law in the kingdom of Resembool that no one may ever interact with the human world.
Everyone followed the rule, well…
That's what he believed.