Hana opened the Prison Realm by using Angel’s technique, Jacob’s Ladder , on its back gate. That forced the seal open and let Gojo out.

What happened

Hana Kurusu was the key because her connection to Angel gave her the ability needed to break the Prison Realm’s seal. The important detail is that the back gate had to be opened, not the front side of the object.

In context

This happens in Jujutsu Kaisen chapter 221, where Gojo is finally unsealed. Several summaries describe the same mechanism: Hana uses Jacob’s Ladder to release the seal on the Prison Realm.

Simple version

  • Hana gets close enough to use Angel’s cursed technique.
  • Jacob’s Ladder targets the Prison Realm’s back gate.
  • The seal opens, and Gojo is freed.