Sukuna takes over Megumis body in chapter 212 of the Jujutsu Kaisen manga. This happens after Sukuna sees Megumis weakened state as the perfect opportunity to take over his body, as he had been intrigued by Megumis shadow techniques from the beginning of the series. Sukuna takes control of Megumis body during the Culling Game, after Megumis sister Tsumiki is controlled by the reincarnated sorcerer, Yorozu. Sukunas possession of Megumis body is a major plot point in the series, and has significant consequences for the story going forward.