I heard the story revolves around the main characters and siblings Eirika and Eiphraim.
Of course it does. They're the main characters after all.
The story, generally, goes like this:
There is peace for a while. The twins, Eirik and Ephraim, rule this kingdom I forgot the name of. Another kindgom suddenly attack their kingdom. Ephraim mysteriously disappears. And Eirik flees to the neighboring kingdom. The rest of the game has to do with collecting these stones, I imagine.
