User blog comment:Hitsuji Mamoru/Servant Creation Room 2 : Guess of the Who/@comment-31726296-20170613015321/@comment-4802891-20170625171436

She is similar to Archer of Nights you say?... Then she could be something turned into a person by the will of Saber?

I'm pretty sure this Saber is Nero, simply because Christianity wasn't a thing when Caesar ruled. Since Caligula isn't a Saber in the Fateverse or just FGO, that only lives Nero (unless there's another Roman Saber Servants I'm not aware of).

However, you talked about Saint Photine? She met her?