User blog comment:Hitsuji Mamoru/Servant Creation Room 2 : Guess of the Who/@comment-27971189-20170613081035/@comment-27971189-20170710043144

This Servant is Fusion / Phantom unique to Alter Ego.

They are not siblings, they are not comrades.

However the lore depicted them as different sides of coin.

They only know each other; barely talks to each other though.

One hate the other, while the other one accepted her just fine.

If I said the origin of the lore, it'll be so easy to guess who are they.