Originally Posted by
mcdoc
Imagination Realization.
As the name suggests, it is the ability to manifest anything you can imagine. I really wish I could do this.
It is the ability possessed by elementals, which are the sense of touch of the natural world. By connecting their will directly to the world, they are able to transfigure the world into whatever environment they imagine.
Of course, the level of manifestation varies depending on the scale of the elemental, and it goes without saying that only nature can be transfigured—things that exist independently of nature are immune.
In Tsukihime, Arcueid eliminated Roa by using marble phantasm to turn the layers of the atmosphere in the hallway into a vacuum, like a carving knife slicing up a daikon radish.
Though she could not affect Roa himself, it was impossible for him to avoid the finely sliced atmosphere, and he was reduced to nothing but ankles. (The gap above the floor was the result of a deficiency in Arcueid's imagination.)
Also, in the world of Tsukihime spiritual realms are not alternate dimensions, but rather exist within the world itself. Things like legendary lands and countries of eternal spring are the products of the imagination of whatever elemental rules over them. Consequently, it is possible for humans to wander into them by accident.
The castle in the mountains that Arcueid calls home is actually a product of her marble phantasm.