How do you get Xiahou Duns level 11 weapon in Dynasty Warriors 4 Extreme Legends?

Defeat Cao Xing immediately. Go all the way Northward across the center water path before Yuan Shu appears (approximately 5 minutes into stage). Encounter Cao Xing after he reappears. Achieve 100 KO Count. A commonly made mistake is to exit the water path before going all the way North. If you go up the stairs on the left side, that would not be all the way North. The correct exit is the stairs on the right side at the North end of the water path. It seems after Cao Xing reappears, you only need to encounter him to get the weapon, but I defeated him anyway. Do this on Expert mode