It sounds like your world is a lot like the Synchro Dimension in my world.

[ Or maybe it's that she comes from the original dimension before it was split in four? In which case that's a bunch of time nonsense... ]

Still, don't underestimate Fusion Monsters! They're pretty tough! I'm from the Standard Dimension myself, but I learned how to Fusion Summon from one of the best.

[ Man, if only Sora were here to hear Yuzu say that. What a good student he has, huh? ]