Sigma asked for more details. It seemed that Flat and the police had formed an alliance and planned to quarantine and examine the girl. As the girl was infected with a virus improved by the Kuruokas, they would act with more caution than usual.
“A hematophage is sleeping by the girl’s bedside, but his reasons are unclear. He did mutter something to himself about using her to bring down Assassin.”
The shadow — now the boy with mechanical wings — related information concerning the vampire Jester Karture. Apparently Assassin’s Master had quite a twisted personality. Sigma listened to the information and considered how he would act.

Fate/Strange Fake: Volume 4, Interlude ("The Parade of Treachery")