In the manga, the duration of Gojo's seal is not clearly defined. It's left somewhat open-ended, allowing readers to interpret it based on the context and events that follow.
The plot of " Defender of the Earth " described how Earth was sealed in the universe. Every Earthling was a sealed god, and Earth became a place of imprisonment. I suggest you read this novel and feel the same destination between the universe and humans. I hope you like this fairy's recommendation.😗
Toge Inumaki is important too. His special cursed speech ability makes him stand out. Also, the principal of the school, Masamichi Yaga, is likely to be important as he is in a position of authority and has an influence on Gojo and the other students. There could be other characters like the members of different clans that also play roles in the complex web of the story.