[Aye, that'll be a game changer in the early parts. Not that Goetia has plans of directly interfering with Mesopotamia given the presence of a certain primordial goddess there.]

Changing events through time travel isn't as simple as it sounds. There are major events [Quantum Time Locks] that are considered necessary for the history of the world, allowing for some variation across other timelines and parallel worlds. Uruk, for example, is one such linchpin: it is one of the most important civilizations from that era, the Epic of Gilgamesh is the world's oldest piece of surviving literature, and King Gilgamesh's life has, ultimately, benefited humanity and its division from the gods.

Now, in order to completely undo human order and anything that might fall under the umbrella of acceptable variance, an incredible amount of mana must be used to both travel across time and distort its events to the point of conceptual annihilation. In a way, our culprit isn't just taking out floors at random - they're targeting both the support pillars and the cornerstones of a building.

[Here, Merlin pauses - this is more metaphysics than he and Watanuki have discussed so far. How well is the youth absorbing all of that?]