User blog comment:Hitsuji Mamoru/Servant Creation Room 2 : Guess of the Who/@comment-31726296-20170527150525/@comment-31726296-20170528062449

Sadly kind of wished I did that. Caster is a normal servant who happened to steal an image/portrait from a goddess who place their divinity/divine concept inside of it.

Here's a hint she was mentioned in one of Hercules'  labour. Not going to mention what labor she was in, where would be the fun in that. Hope this helps.