Hey there, if you're stuck for things for your characters to do in Ultimate Crossover, then Nia, assuming she's still in the lab, could ask Fate some questions. She always seemed full of those in the anime, so that would certainly work. As for Namine, you can have her chime into Kakyoin, Magashi and Tsukasa's conversation at any time, it wouldn't be a problem. No suggestions for Karkot though, since I don't really know enough about him. The hotel he was in was destroyed, so he should probably wander around the town and meet with Ichigo and his group for now, unless you already have any plans.