Rostam was friends and rivals with Arundolyn, forging a bond strong enough that, after he was slain in battle, Arundolyn never entered combat again out of grief.
Rostam wielded a sword in battle, and his combat style is still practiced by the Knights of Favonius to this day. He also mentored the White Knight, whose pursuit of uncompromising justice eventually turned him into the Bloodstained Knight.
Rostam and Arundolyn spent most of their childhood together, first as rivals and then as fellow knights and close friends. He also fell in love with a maiden back in Mondstadt, and was the mentor of the White Knight.
Despite being a Knight of Favonius, Rostam did not shy away from doing dirty work in the background — it is said that he even inherited Kreuzlied's secret society, which was formed 1,000 years ago to help Vennessa overthrow the Aristocracy.
After the fall of Khaenri'ah's Eclipse Dynasty and the cataclysm that followed, Rostam embarked on an expedition with the Knights of Favonius to exterminate monsters that spewed forth. He died in battle, however, bringing an end to his career as a knight of Favonius after 23 years of service.
Following his death, Arundolyn never took up the sword again. Meanwhile, the maiden he fell in love with returned to her hometown in Mondstadt only to find it destroyed by monsters and Rostam dead. Out of a desire for revenge, she used liquid fire to transfigure herself and became known as the Crimson Witch of Flames.
- Rostam was a mythical Persian hero. Among the mythical figure's achievements is slaying an azhdaha; however, there is currently no known link between Genshin Impact's Rostam and Azhdaha.