Jotaro Kujo is the grandson of the previous JoJo’s Bizarre Adventure protagonist, Joseph Joestar. Jotaro severely injured four gang members one day, leading him to believe he was possessed by an evil spirit because he’d never demonstrated such strength before. His grandfather arrived after he turned himself into the police and explained what was going on. DIO, Joseph’s grandfather Jonathan Joestar’s vampiric adoptive brother, has reawakened and gained a Stand, a manifestation of his fighting spirit that he can summon, and because DIO’s head is attached to Jonathan’s body, the rest of the Joestar bloodline has awakened Stands on their own.
However, Jotaro’s mother also awakened a Stand, which was gradually killing her due to her inability to control it, which was caused by her unwillingness to fight and her gentle nature. As a result, Jotaro, Joseph, and other Stand users travelled to Egypt to defeat DIO and save Jotaro’s mother.