Sui-Tang: My Brother Is Cheng Yaojin

A young man from modern times finds himself in the body of Cheng Xiaotian, Cheng Yaojin's younger brother, who was born with extraordinary strength but is mentally disabled. He overcomes his disability and gains the strength of five dragons. Using his modern knowledge, he helps Cheng Yaojin rob the imperial tribute and escape danger, then joins the Wagang forces to protect Qin Qiong and the others before eventually serving Li Shimin in the Tang court. He builds fortified camps at Hulao Pass, changes weapons to fight the Turks, and uses brute strength and ingenuity to overcome one challenge after another. He also proposes opening up wasteland for farming and improving forging techniques, ushering in a new era amid the chaos of the Sui and Tang dynasties.