Instructions
Preparation
Get a good fourth weapon, ideally with two or more bonuses at +20 or better.
Power him up all the way or reset his stats to make enemies easier.
Obtain the Battle Drum. You'll need it.
Bring a companion. This will help a lot.
The Battle
Start Masamune's Attack on Honnouji stage on Hard difficulty.
Be aware that if any of your allies die, you must start over.
Head south and eliminate the defense captain.
Go inside the fort and eliminate the defense captain.
Head to the eastern side of the temple and defeat the defense captain that shows up.
Head all the way up north and defeat the defense captain that comes to greet you.
Get to the blue X before the Akechi army breeches the walls.
Save your game.
Begin eliminating officers. Try and lure them away one at a time.
Defeat Mitsuhide Akechi when he gets near.
Defeat the Oda officers, leaving Keiji Maeda for last.
Defeat Keiji Maeda. The supply unit should appear near the center of the map.
Defeat the Supply Captain for your weapon.
Save again.
Go defeat Nobunaga and enjoy your massive Mikaboshi swords.