When you beat East's section of the game you get to view the war route you took from the main menu, you also get to play as the west in your nest new game. When you beat that part you get the choose battle mode on the main menu. You can play any battle that you have done and choose to be the east or the west.
Play with the West
Finish a game with the East
Get Battle Mode
Finish the game with the East & West
To get Musashi play through the game as the East until mission 5. When you get to mission 5, beat it without losing a unit or a commander losing a duel.You also cannot have lost a mission before>