Satoru Gojo is Jujutsu Kaisen's most powerful character, with the power of Six Eyes and Infinity. During the Shibuya Incident, he was sealed in by Geto as it was not possible to defeat Gojo in a normal battle. Gojo is trapped in the prison realm for 1000 days before he is rescued by Itadori Yuji and his allies.
Gojo is finally able to escape the Prison Realm with the help of Angel, a mysterious character who can erase any cursed techniques. Therefore, with her powers, she nullifies the Prison Realm. They successfully unlock the curse, and Gojo is freed.
Geto convinces Mahito to team up and seal Gojo. They attacked Shibuya, and Mahito, Jogo, Hanami, and Choso worked together to blindside Gojo.
In the meantime, Geto worked on activating the cube, and when the time was finally right, the Prison Realm appeared suddenly behind Satoru. He tried to flee, but Geto pulled a sly move, revealing himself for the first time since the original Suguru Geto's death.

After this event, the balance of the world in Jujutsu Kaisen is shaken. With no Gojo to stop evil, Kenjaku and other antagonists have a clear path to unleash chaos. During this incident, multiple sorcerers died, and an entire section of the city was annihilated.
Eventually, Kenjaku announced the Culling Game in Jujutsu Kaisen, a twisted survival game that forced Jujutsu sorcerers and cursed users into high-stakes combat. He did this to fuel a massive ritual in which he could merge with master Tengen, which would give Kenjaku godlike powers. It became very important to free Gojo to stop Kenjaku from being successful.
Yuta, Itadori, Angel, and the others finally put their plan into action to unseal the Prison Realm and free Gojo. They used the help of Back Gate instead of Front Gate.

Within the Back Gate, Angel activated her cursed technique called Jacob's Ladder, which has the nullification ability, effectively erasing the seal that had kept Gojo trapped since the Shibuya Incident. It was an intense process, but Gojo Satoru was finally released.
Gojo steps back into the world during one of its darkest hours. Without wasting time, he understands the new situation he is in. Sukuna is now inside Megumi Fushiguro and now possesses the power of both the Ten Shadows to go with his own.
Shortly after escaping, Gojo now has to face the King of curses- Sukuna in a duel filled with Domain Expansions, strategic counters, and moments that redefine what jujutsu sorcery can be.
What is the Prison Realm in Jujutsu Kaisen?

Prison Realm in Jujutsu Kaisen is a special-grade cursed object. It can seal absolutely anything or anyone in a pocket dimension. This object is referred to as a taboo object, and it is a living barrier so powerful that there is nothing it cannot seal. Moreover, it is the final remains of the Buddhist Monk Genshin.
There are a few conditions to activate and use it. When given the command by chanting the incantation "gate open" (kaimon), the cube opens and stretches into a mass of flesh, pulled by four corners, with its remnants clinging to the edges.. For the target to be sealed, they need to be within 4 meters of the cube for a minute's worth of time within their mind for this cursed object to hold on.
Finally, when these conditions are met, a mass of flesh pierces the target, rendering them immobile and removing access to their cursed energy. Then, there is a second incantation, "gate close" (heimon), and the Prison Realm goes back to its original form, sealing their target inside indefinitely.
Gojo's escape marks one of the most pivotal moments in Jujutsu Kaisen, leading to a chain of events that changes the story's trajectory forever. Although his time post-escape is short, Gojo’s impact lingers for the rest of the story.