Imagine that you wake up outdoors and crouched down in front of you is a school girl pointing a sniper rifle at a fellow student, who apparently is the enemy, standing across the courtyard. This same girl who’s wielding said sniper rifle then tries to recruit you for a group she fronts during which time you have been informed that you’re now in the afterlife. This is exactly what you can expect in the opening scene of Angel Beats as you follow the (very unique) journey of Otonashi who has no clue what’s going on coupled with the fact he has amnesia & doesn’t remember anything about himself. (Not exactly the greatest condition to be in given the circumstances.)
As you may have guessed Angel Beats surrounds a group of students trying maintain a strong opposing force against Angel, the girl I mentioned who was having a sniper rifle (unbeknownst to her) waiting to deliver a shot to her cranium, in a world that could be best described as unique version of the afterlife that is confined to the grounds a high school. The goal of the students is simple: remain in that world. If they cause an imbalance on how the things should run or perhaps how they conduct themselves in certain situations, they will likely be met with consequences (usually Angel, who coincidentally is the student council leader, coming along to dish out some punishment) or perhaps even being ‘obliterated’.