There's no such thing as emotion There's no such thing as emotion I know that sound's like a strange and ironically logical statement for me to make, but often times a statement doesn't need to be true. It just needs to be said. When dealing with character's that have little to no emotions it's very hard for a writer to get it logistically correct. This is why, for every single character and creature I write about, I stick to one universal truth that is unshakably simple. What is your character's motivation? As a writer one must be able to act out the various roles of all the characters in his mind. What they are feeling and what their motivations are. For your stoic character you must psyche your very mind to think as he does. Normal lifeforms feel first, but your character must simply be driven by pure motivation like a logical computer. After he's considered his motivation than and only than can he consider what little emotion you want him to have. You see it's simply a matter of organizing your thought process while writing him. Try the process out and tell me if you see and differences.
His initial reason for supporting the big bad is loyalty, however that's before he gets rid of his emotions. After he does that the plan is for him to lose everything emotion wise except ambition and the self-preservation instinct. So his continued service of the big bad is only through him thinking it's the most logical thing to do to get power. He may also have curiosity, or at least the ability to wonder what's going on.
Your idea kind of reminds me of these masked warriors in The Chronicles of the Raven. I can't remember what their called, but they belong to the Dark Mage College. When they were babies their souls were given to the mount and they (normally) grow up and never learn of it. When they die (or get to a certain age at which point their souls are taken by demons) and put into a soul tank. They become obidiant soldiers of that College and do as its mages command.
