OUGHHHH RIGHT IT'S SO SO SO SO GOOD. that's what i love most abt alterego cain like he doesn't have his trained-since-childhood chivalry and knightlyness to hide behind the way he does in canon. it's honestly interesting seeing him in such a similar position as he has in canon except for specifically without the knight aspect. like he's still serving someone he considers his savior after having fought as a hero for the people, the basic outline is the same as his relationship with arthur, but i guess the primary difference is like...alterego cain doesn't feel as beholden to social status as canon cain. like canon arthur keeps saying he wishes cain wouldn't treat him as his lord but as his friend, whereas alterego cain............ well he doesn't treat snow like a civilian, but there's less of a sense of there being an insurpassable boundary separating the two of them. he's a little more relaxed, i guess you could say?

my favorite favorite FAVORITE part of alterego cain is exactly what you point out: his willingness to kill but also protect. to blindly follow snow even without clear instructions on why he's following him. these are actually things canon cain is 100% willing to do for arthur, but in alteregoverse he's so...open? about it? he doesn't have the knightly facade he can hide behind, plus the fact that arthur would typically disapprove (which doesn't even stop him at certain points. i love pointing out knight event and cain's willingness to kill hector, a teenager he knows, if that was what things called for), so he just doesn't hide that at heart he is willing to trace the clear, ruthless line from a to b in the name of the person he'd decided to give his life to.

moving AWAY from cain dissection for a second though i actually really DO love his dynamic with snow. i love love love that snow is willing to share white's secret with cain instead of just getting rid of him on the spot. i love that snow trusts cain with white in general!!!! i love that cain is white's playmate and babysitter and helps him take his icky sleeping pills and that snow trusts him to do all of that faithfully and carefully and safely even though he already lost white once already. that's an absolutely huge gesture from someone like white, and cain dutifully and happily ensures he won't let his master down. i like them so much

i'm nnnnot really a fan of cain and arthur's dynamic in canon specifically because of the fact that arthur refuses to see the ruthlessness that cain does in his name, but here snow is perfectly well aware of it and in fact values that ruthlessness, so. i admit i like alterego snow and cain's dynamic a lot more for having that important variation