Tsubaki herself did not understand why she had so readily accepted the black grotesquery.
Despite her youth — no, precisely because of her youth — there would have been nothing strange about her following her instincts and embracing fear. For some reason, however, Tsubaki had never felt afraid. It was as if she sensed that she could be safe with the thing. And, because she never questioned that fact herself, there was no one to consider the affinity between her and the black mass.
Not until that day, that moment.
“Hey, can I pet your dogs and cats too?”
Tsubaki was surprised at being spoken to so suddenly. When she hurriedly spun around, there stood a boy she had never seen before. He looked a few years older than Tsubaki, although from an adult perspective they would both be considered young children.
“Umm... Yeah. Sure!”
Tsubaki, while hesitant, cheerfully accepted the boy. She had not noticed that the moment he appeared, the black shadow — Pale Rider — had swelled up as if it was on guard, then returned to its normal size in apparent relief as soon as he smiled at the boy.
The boy, on the other hand, did remark the wriggling black mass, but let out a sigh of relief when he saw it relax.
Thank goodness. It’s determined that I’m Tsubaki’s friend. That was close; even I can’t perfectly predict the actions of a system-type Servant, the boy thought as he stroked a dogs cheek and flashed Tsubaki an innocent grin.
“Jester.”
“Huh?”
“My name’s Jester Karture. Pleased to meet you.”

Fate/Strange Fake: Volume 4, Chapter 10 ("Day 2")