Have you seen Katekyo Hitman Reborn? The plot of the best arc, the future arc, involves someone who gains the knowledge of the other worlds and sets out to conquer them all, turning some of them to wastelands. I would recommend that show just for that arc, it has a good plot and great fights, and though the beginning was slow, it turns out that what I thought was filler was actually diligent build-up. Anyway, I think it would be interesting to have a connection between the different worlds similar to what I'm discussing, just throwing it out there.