Symbolism, Imagery, Allegory
Remember how weird it is when Ky starts crying in the middle of that hilarious movie about bombing people? Once he starts sharing his life story with Cassia via drawings, she sees one with his mother and father lying on the ground. Ky stands next to them, looking up at the sky, where "'the rain has turned to something solid. Ammunition, I think. I've seen it in the showing'" (20.46)—ah, so that's why that movie was so upsetting. Cassia says:
Death came from the sky, and that's what he remembers. Every time it rains. (20.51)
It's pretty powerful—and pretty unavoidable—stuff. And because every time it rains Ky is reminded of bombs raining down on his family and killing his parents, we are clued into how insidious Society is. Ky can't forget the damage they've done.