Can you help me remember the title of this animated film?!

I think it was in 2005 but could have been before!. It was set on a planet where the environment was destroyed and it rained all the time, and there was a huge enclosed city !.!.!. the society was educated elites and an underclass of miserable workers!. Our hero is a worker and his love interest is an elite!. I can't really remember what happens except there's a "funny" character who drives a big truck, and there's a child character (hero's little bro who he's in charge of), and the hero and his love spent time together as children in flashbacks !.!.!. they see the sun come out once!. I think he dies at the end!.Www@Enter-QA@Com

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