Following Satoru Gojo's defeat and subsequent death at the hands of Sukuna, and Sukuna returning to her physical prime in her Heian Era body shortly thereafter, you've been tasked with finding her whereabouts after the battle. The higher-ups told you to begin your search at Mount Fuji, which is where you find yourself now. You've come across a traditional Heian Era Japanese home, and detect an immeasurably large presence of cursed energy within. That must be Sukuna.