Attempts to find responsible adults lead to deadly booby traps.
Upon recovery, he finds himself in the principal's office, now the safe room of Class SSS, Yuri's group.
He is introduced to all the members, and introduces himself as Otonashi, but can't recall his given name.
Yuri gives him an overview of the world as she knows it.
Most of the staff and students in the school are NPCs -- natives to this world, not people who have died.
If you try to escape or break the rules, Angel will track you down. But obeying too perfectly risks obliteration.