“Yes... but I think you’d better head back for now. If this was a video game, it would definitely be
asking you if you want to save right about now.”
“I concur. My apologies, but I have no desire to proceed further without making preparations.”
Flat’s senses weren’t alone this time. Transforming into an ordinary person had significantly lowered Berserker’s abilities as a Heroic Spirit, but he could feel it too. A dense, ominous aura was swirling around the door that lead from the decontamination room to the sickroom.
“If the stuff that spread into the hallways through the decontamination room is a black fog of magical energy... then what I can see in the entrance to that room is part of a giant waterfall.”
Berserker could not see that clearly. But, although his true identity was unknown, he had manifested as a “killer,” and all his killer instincts were raising an alarm. They were warning him that the sickroom was filled with the same air that must have surrounded him in the fogs of London. They were warning him that ahead was Death itself.

Fate/Strange Fake: Volume 3, Chapter 9 ("Day 1, Evening")