Tuo Yuwen, a descendant of the Northern Zhou Dynasty royal family and the son of the Northern Zhou Emperor Yuwen Chan, was usurped by the Sui Dynasty because of his country. He lived among the people since he was a child. Fortunately, Su Yang, a famous soldier in Sui Dynasty, discovered him and saw his qualities, so he accepted him as an apprentice and his younger brother Yang Yichen accepted him as his adopted son.

Yuwenmen has been guarding Xuanyuan Sword for generations. When Tuo Yuwen was twelve years old, Yang Di sent Su Yang to attack the Northern Zhou Dynasty in order to seize the Xuanyuan sword, and his father died to protect him.