However you can only use it once and connect one fantasy world that you come up with. Once you do that then the worlds are merged forever. So use this power wisely.
After much deliberation (a whole lot of it), i would use the power to connect this reality and the Tensei Shitara Slime Datta Ken one.
Mostly because it would modernize Tensei's world a bit, and at least, everyone gets a shot at "special abilities", if they work for it. Genetics won't be the only factor, work will be too.
Isn't there something about angels coming in every once in a while to destroy civilization and reset all tech? I think it's also sped up by technological progress, so they could start descending right after or a little time after the merging.
