The Legend of Qin Season 1 Episode 8 E 8

Gai Nie and Tian Ming begin to explore the Mechanical City with their Mohist allies, and quickly learn to watch their step since it has automatic - and deadly - defenses if they stray off path. They meet Dao Zhi, the quick-footed King of Thieves, who helps them navigate the traps. As they reach the inner part of the city, they are greeted by Teacher Xu, the Mohist's greatest swordsman. He recognizes the sword Yuan Hong and tells them that although he is a master swordsman and swordsmith, the creator of that blade makes him look like a beginner. He also reveals that the creator of Yuan Hong was his mother. Meanwhile, Wei Zhuang and Emperor Qin finalize their plans of their attack on the city.