This journal's AU is actually "Neku didn't improve so Josh erased Shibuya in the end", though I don't think I've had the chance to play this particular Joshua off of another Joshua. (Lots of Nekus though. It's usually a love/hate/mostly-hate thing with OU Nekus.) At the risk of being predictable, I could go with this one? He'd be certainly curious to see how a Joshua from a world where Neku didn't try to shoot turned out.