While Sigma was busy questioning himself, Assassin activated one of her Noble Phantasms.
“Sink into a dark prison . . . Meditative Sensitivity: Zabaniya.”
A perception-type Noble Phantasm that attuned her to the surrounding space as if she were the world’s shadow and sensed nearby currents of magical energy and wind.
Using those currents, she attempted to locate either the “giant black shadow” that seemed to be controlling the giant, three-headed dog, or the hematophage who must be connected to this world.
“. . .?”
What she found, however, was a different current of magical energy.
It was giving off a strange current, as if to disturb the balance of magical energy throughout the entire city.
It was an infinitesimal current. Without her Noble Phantasm, she would not have been able to detect it.
Is this . . . magical energy leaking out?
No, leaking in? Or is it . . .
The flow was like the whole world was breathing magical energy through that one airhole.
She paused briefly, wondering whether to pursue the giant, three-headed dog, but ultimately decided to follow fluctuation of magical energy.
She thought that where it led was simply too symbolic and might even offer a hint to escape that world.

Fate/Strange Fake: Volume 6, Interlude ("A Mercenary is a Free Man I")