User blog comment:Hitsuji Mamoru/Servant Creation Room 2 : Guess of the Who/@comment-27971189-20170613081035/@comment-27971189-20170710130504

They're character from a lore in Europe.

They're not mystical creatures like Medusa, they are Human.

Their appearance as combination Servant stems from "Its impossible to talk about one of them without bringing the other one".

Funny story, both can be considered one but one person; share similar interest, and this interest is what caused the main female (who talking first) hate the other female (second one).