Instructions
Preparation
Get a good 4th weapon, ideally with 2 or more stat bonuses at +20 or better.
Recruit some help. Attaining ultimate weapons is nearly always easier with a friend.
Reset if you have to. Enemy difficulty level is based on the average level of the players. The lower your level, the lower the enemy's. With a good weapon and items in your corner, this means you can make short work of weak bad guys.
Make sure you have completed Oichi's story mode.
The Battle
Start the Battle of Anegawa on Hard difficulty. Seriously, have you ever done one of these on Chaos? Neither have we.
Take a deep breath. Why? Because the following is the hard part.
Complete the missions as normal without letting any of your officers die. This is where a friend comes in handy. Have them keep your soldiers alive while you complete the missions. Think it's crazy? That's really all you have to do!
Catch the Supply Unit that appears in the southwest.
Defeat the Supply Captain for the weapon.
Finish the stage. Easy, huh?