Cai Fu is nicknamed "Iron Arm" because he can chop off a prisoner's head with just one swing of the sword saving the person unnecessary pain.
However, Liangshan's Chai Jin also visits Cai Fu and offers him an even larger sum of money to ensure Lu is safe.
However, Li Gu bribes the guards escorting Lu Junyi to Shamen Island (沙門島; present-day Changdao County, Shandong) to murder him along the way.
Just when Cai Fu is about to swing his sabre to chop off Lu's head at a public execution ground, the brothers are gladly stunned by Shi Xiu of Liangshan, who storms towards them in a lone attempt to save the squire.
He participates in the campaigns against the Liao invaders and rebel forces in Song territory following amnesty from Emperor Huizong for Liangshan.