In Assassin's Creed Mirage, Basim Ibn Ishaq is a street thief before joining the Hidden Ones. He lives in ninth-century Anbar and survives through theft before his ambitions bring him into contact with the Hidden Ones.
The game depicts Basim's recruitment and training under Roshan, an experienced Hidden One. His early life as a thief explains his agility, urban knowledge, and familiarity with Baghdad's streets, while the Brotherhood gives those talents a disciplined purpose.
Mirage is set primarily in ninth-century Baghdad during the Islamic Golden Age. It focuses more tightly on stealth, investigations, contracts, and social infiltration than several of the series' large role-playing entries.
Basim had already appeared as an important character in Assassin's Creed Valhalla, but Mirage serves as his earlier origin story and follows his transformation into a Hidden One.