Originally Posted by
TresserT
More baseless speculation:
Marisbury wants to achieve True Magic (or more accurately, he wants to reach the root). In Melty Blood Actress again, Osiris states that Zepia was 1 step away from achieving the sixth true magic. As a reminder, Zepia's plan was to take over Arcueid's body and use Marble Phantasm in order to create a future which he was unable to calculate.
This made me think, U-Olga basically has Marble Phantasm. She can simulate events, and once those events are simulated she can superimpose them onto reality. This is how she revives the crypters- Kirschtaria has to prove that it's possible for them to survive, then she can make it so they do survive. Olga's power is that anything which is possible, she can make into reality.
My proposition is that this is Marisbury's goal, and the sixth true magic. The power to make anything which is possible occur. On paper this sounds like a weaker version of the second magic, but we've already seen how it's not- the second magic can only access parallel worlds, and due to the pruning phenomenon, not all "possibilities" are "real". This hypothetical sixth magic allows Olga to do things like create Lostbelts- things which are hypothetically possible, but could never actually exist.
As of right now, Olga is only capable of doing this sort of thing on a simulated planet (CHALDEAS). And this is why the plot of the game occurs- in order for Olga (following Marisbury's design, though she might be unaware of that) to actualize the sixth magic, she needs to create a world egg from his simulation. That is, she needs to perform a Reality Marble on the whole world- swap the "inner world" of CHALDEAS with the outer world of reality. In other words, hollow out the planet.