It is the way he talked Rouge, it gave off the feeling that the Archer had a good history with him. I'm not too familiar with summoning and all that but I do know with the whole ideals of a "Master and Servant duality" from my Titan Chryses. More I think of it, it similar to us pilots. With out a Titan or Servant in this case, the Master or pilot is defenseless, the last time I was with out my Titan... two Apex Predator pilots jumped me and cut off my arm in a form of sick trophy, I got the limb to prove it.
He shows Rouge his arm which is a semi human prosthetic which was cleverly hidden under the digital green camo shirt and glove.