Satoru Gojo gets sealed in the Jujutsu Kaisen manga in chapter 91, during the Shibuya Incident arc.

If you’re reading the anime instead of the manga: this sealing happens in the Shibuya Incident storyline, when the Prison Realm is activated and closes around Gojo after Kenjaku (in Geto’s body) distracts him.

For extra context: Gojo is later unsealed in chapter 221, when Hana Kurusu (Angel) uses her Jacob’s Ladder technique on the Prison Realm’s back gate.

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