Stage - Battle of Nanjun Difficulty - Hard or Chaos Character - Zhou Yu
Requirements: Rescue Gan Ning within 5 minutes of the stage.
Pretty self explanatory, just head straight for Gan Ning and rescue him in under 5 minutes.
Note: You may need to rescue Ling Tong, I took a gamble and chose not to.
As requested here's the unlock guide for Zhou Yu's 5th weapon "Crimson Cloud" if you have a request feel free to ask and I'll do my best.