“Are you well? You look quite tired.”
Without warning, the man from the opera house appeared in a corner of her cell. “!?”
Startled, Ayaka shot upright. The man who had entered unnoticed called out to her again. “Don’t act so surprised. Passing through walls is nothing if I shift to spirit form. My interrogation's been put on hold. I was put in a cell a little farther down, so I came to check in on you.” The man had easily penetrated the locked isolation cell. Perhaps he really was some kind of spirit.

Fate/Strange Fake: Volume 2, Chapter 3 ("Day 1, Early Dawn")