You can watch this on Netflix if you're a normies or cheap, or Crunchyroll if you're a weeb who likes spending money.
The opener is unusual in that the piano part of the music is being played by one of the characters on a Grand Piano.
Otherwise, shots of a number of characters, in high school uniforms. They seem more... armed... than most high schoolers.
The pianist has angel wings.
The official release has subtitles for the opening song.
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Our boy jerks awake on a hard cement floor. He doesn't remember anything.
A girl nearby asks if he's up yet. She can't check, on account of being glued to her sniper rifle's scope.
She bids him welcome to the Not Dead Yet Battlefront.
She invites him to enlist. This is the afterlife, but you'll be obliterated if you don't fight.
The patch on her shoulder says "rebels against the god".
This is Yuri Nakamura, leader of this faction. She says her enemies are angels, but at first blush the person she's aiming at looks like a normal girl.
Our boy thinks she might not be a good guy.
He rebuffs the recruitment and tries with the alleged angel.
She denies being an angel and declares that she is the student body president. But she confirms that everyone here is dead.
Our boy concludes this is all a trick and challenges her to prove it.
She materializes a blade and runs him through.
He wakes up in the school infirmary.
He's uninjured, but the blood on his clothes tells a different story.
Another boy wielding a halberd comes to visit. And by visit, I mean kill him 100 times for the personal insult of not joining Yuri's group.
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.
Otonashi is mostly buying time. Amnesia is common among new arrivals, but memories return eventually. He'll wait until he remembers who he is before he really decides to stay with this group.
They prepare their next mission: to steal cafeteria lunch tickets.
The plan goes like this: the distraction squad will put on a rock concert, then, at the height of the concert, they'll activate a giant fan, blowing all the lunch tickets in the cafeteria out where they can grab them.
All Otonashi has to do is hold off Angel.
Too bad she's invincible. When she comes up against him, she can parry his bullets. When the others back him up, she activates a shield that deflects them.
They buy enough time for the operation, but deal basically no damage to Angel.
The team makes a pilgrimage to visit The Guild, an underground weapons manufacturing facility.
But Angel is closing in on them.
Creation in this place is not actual manufacturing, but reification of memories.
They scuttle the factory to keep Angel from getting it.
But the workers, with their knowledge and memories, escape.
Yuri tells the (horrible) story of why she decided to fight against God.
Iwasawa (the band/distraction leader) tells the story of her life and death.
She was saved from a brutal home life by music, but that salvation was betrayed when a head injury left her mute and paralysed.
She's poured her whole self into a new song, but as a ballad it's no good for distraction.
The band puts on a concert while the others, with the help of the hacker known as Christ, infiltrate Angel's computer to learn more about her powers.
The authorities shut down the concert and start to confiscate the band's instruments.
Iwasawa plays her ballad over the PA system on her acoustic guitar, and vanishes, her last wish completed.
Yuri reveals that Angel is developing her powers the same way they make weapons.
With the loss of the lead singer, the OP changes. Nice.
The gang participate in a baseball tournament. But if they win against Angel, will Hinata disappear because his issues are resolved?
Expect the Spartan response: If.
TV Tropes tells me that Everyone Is Jesus In Purgatory is an overactive imagination searching for Deep Meaning in everything.
The show summary tells me it's intended to be purgatory.
Let's see how it goes.