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.