Bebop refernce. - Fullmetal Alchemist and the Broken Angel
While fighting Armstrong and Mustang you probably were not paying attension to the background music. If you lissten correctly you will see that it's the Cowboy Bebop ending theme.
Please do not be rude to others, what may be obvious to you may not be to the person asking the question.
Also on: Gameboy Advance, check out those pages for more help with this game.