It tended to be assumed by people that Roy Mustang had always had the corner market on instigating questionable activity, but Maes had started his fair share of pranks in those early years; certainly not limited to terrorizing their parents and neighbors, they attacked one another viciously, but usually laughed over the end results together. Never a dull moment, indeed - inseparable, Roy and Maes ruled the playground by day and their houses by night, and flashed messages via a secret code out their windows at each other after lights out.
While they never quite grew out of the pranking stage, sensibility started creeping into the edges of ther lives soon enough; there was no future in a dying town. But it was Mustang who first announced his chosen path.
"I'm going to be in the military when I grow up," Roy said to Maes as they threw rocks into the swimming hole.
"Why? That sounds boring," Maes answered, hefting a big rock with both arms. It made an appropriately big splash as it hit the water.
Roy grinned. "'Cause I'm gonna rule the whole wide world," he said with dedication.
"Then I'm gonna rule the world, too," Maes replied, because he and Roy always did everything together.
"You can't rule the world if I rule it," Roy answered sensibly. "We'd have to take turns. I promise I'll let you have a turn after I'm done."
They shook on it.