The first season is a horror-action show about humanity hiding behind walls, and it’s very good at that. Then the story keeps opening up. Each season answers questions and raises bigger ones, until the conflict looks completely different from where it began.
It’s grim, and it asks you to sit with uncomfortable ideas instead of cheering for one side. Not everyone likes where it ends up, but few anime are this ambitious or this tightly built.
Watch it in order and avoid spoilers online; the reveals are a big part of the experience.

