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.
I'm not entirely sure as I haven't read it specifically. But generally, it might be about a battle or conflict between the character Dredd and the concept of death. It could involve Dredd facing death - like challenges, maybe some high - stakes showdowns with death - related entities or situations.
Since I haven't read it, I can only assume that Dredd is one of the main characters as it's in the title. There might be other characters like his allies in the law enforcement or the antagonists who are related to the 'death' aspect in the story.
It's hard to pinpoint exactly where Gojo is at any given time in the manga. His whereabouts change as the story progresses and different scenarios unfold. It could be in a supernatural realm, a mission site, or interacting with other characters.