官渡 – 秘蔵武器獲得戦・焔刃剣
Blaze Sword Hidden Weapon – Defeat Dian Wei.
This battle can only be accessed from Free Mode – Guan Du stage.
Also note that this requires Patch 1.03 and above in order to play.
1. Head north and defeat both Xiahou Dun and Xiahou Yuan.
2. Entering Guan Du will trigger Dian Wei as a reinforcement on the west edge.
3. Defeat him and he will drop the weapon box.