Yeah, Simon drills down into the underworld to bring Kamina back. But Kamina also brings back his new friends from the afterlife: Spike, General Leo, Shirley, and his new bitch Aerith.
Yoko is jealous of Aerith at first, but then she gets over it and hooks up with Simon. Nia doesn't mind that, cause she's already hooked up with Leo at that point.
While Simon and Yoko are beating down Genome, Spike totally kills Rossiu, just for the hell of it. Kamina high-fives him for it, and the show ends with Simon and Yoko making out in Lagann.