Haruri’s Servant, rendered invisible by magecraft, had stationed itself in the courtyard.
Because it had absorbed rubble from Bazdilot’s workshop, which it had destroyed, it actually put more strain on it to dematerialize, so they were getting by with invisibility magecraft and magical-energy concealment.
The woman who called herself Ishtar seemed to still be able to perceive the Servant clearly, because she looked up into the courtyard through a glass wall and said:
“Don’t you think so too?”
In response, a sound like the grating of a massive ship’s propeller rang out from the courtyard.

Fate/Strange Fake: Volume 6, Chapter 18 ("As Dream and Reality are Both Illusion I")