Author's Note: This is a FMA/HP crossover where the worlds naturally coexist. I did it this way to stand out from other HPxFMA crossovers. Also the events of Brotherhood and the manga happen at the same time as Goblet of Fire and end at the same time of Deathly Hallows. In 1997 Ed and Winry give birth to their kids. Now I am not going to make Ed a bad parent by abandoning his kids, so I am going to make Roy Mustang team up with Harry and the gang instead. With that being said, on with the show!

Central Command, 1999

With Ed raising the kids with Winry and Al going to Xing with Mei, Roy Mustang's journey had begun. He spoke to Fuhrer Grumman about what to do.

"Fuhrer Grumman." General Mustang said. "My chessboard is broken up, and Riza left me to train with Olivier in Briggs, so I need a mission."

"Well, you can go to a place called Hogsmeade to protect a boy known as Harry Potter, the hero in the Battle of Hogwarts." Grumman said.

"Ok then." Roy said. He went off through the halls of Central Command, and ran for the elevator. On the elevator, he planned to go to the ground level, but accidentally pressed a white button that led underground. The elevator took him to a lower level right below the center where Father sat. He arrived at a secret passageway.

"This is weird." Roy said to himself. He moved through the passageway and found a train that goes on water, much like the Sea Train from One Piece, except it used a canal as railroad tracks and acted like a subway. He took the train and it sailed through the canal, all the way from Southeastern Europe where Amestris was, to Scotland, where Hogsmeade was. Roy got off the train and went to see Harry and his friends. Roy saw Harry, Ron and Hermione getting a butter beer without them knowing.

"They look like they are getting something to drink." Roy said. "Time to make a house call." Roy followed them into the Three Broomsticks and saw them drinking Butterbeers.

"Hello strangers." Roy said.

"Who are you?" Harry asked.

"No need to fret." Roy answered. "I am Roy Mustang. I am a friend."

"How do we know we can trust you?" Hermione said.

"I come from Amestris, which is a nation linked with the British Ministry of Magic for over two hundred years." Roy explained.

"Go on, tell us." Roy sat down to tell the story.

"Long ago, there was a philosopher from Xing known as Leonidas of Darkness, or Leonidas Hermes Mustang ." Mustang explained. "Originally from Xerxes, he moved to Xing and from there he went to bring magic to the British Wizarding World."

"Wicked." Ron commented.

"There's more." Roy explained. "He worked with Slave 23 or Hohenheim of Light to create the Homunculus Father back in Xerxes, and created an elite team of guardians known as the Death Eaters."

"Wait, so the Death Eaters were intended as guardians?" Harry questioned.

"Yes and no." Roy answered. "The first iteration of the Death Eaters were, but Voldemort had corrupted them, creating his own iteration of the Death Eaters that replaced the old iteration entirely."

"So what happened to Leonidas?" Hermione asked.

"He went on to be known by another name, The Lightning." Roy explained. "A dark mage with raw destructive power that could shatter a whole country."

"Hey!" Hermione said. "I remember the Lightning! I was reading about him in History of Magic in my third year."

"Then you have done your homework." Roy said. "Come on, we have a world to save!" Roy went with Harry, Ron, and Hermione as they journeyed on their quest to defeat the Lightning.