Kanshin planed the unexpected idea to overcome the army of Chinese state of So (Chu).    

His troop pretended to attack the fortress of So and then run away from the fortress. 

Then, So’s army pursued Kanshin’s troop and resulting in no soldier in the fortress. According to Kanshin’s order in advance, the 2,000 soldiers carrying red flags army took advantage of the situation to hang their flags on the fortress. 

When seeing such a sight, So’s army believed to lose their fortress.