Promies and Giester..?

I have been having trouble finding a group since I have recently gotten out of the Marines. So I am in the position of STing for a group that minimal is just myself and at max is my wife and my closest friend. I purchased all of the nWoD books from DTRPG and the interests of the "group" (if that IS what you would call it :P) Giest and Promethean. So, now my conundrum is this, has anyone successfully ran a collaboration story with allied Giester and Promies? If so, then perhaps you would share some insight as to how an entity of death and a creature striving for mortality can work together. As Giest is so new there are no stereotypical comparisons of the two creatures.

Well they are a couple of quick ways to make interactions seem non forced.  Using an ulgan promethean for example, or making the Sin-Eater a redeemed promethean.

   Or Geists are some weird cross between spirits and ghosts, what if the sin-eater's geist is a cross between a ghost and a qashmal?  The sin-eater would have a qashmal's driving purpose. 

   If you'd like something more mondane, they could just know each other.  Perhaps they died together, one got offered a second chance by a Geist, the other was used to create a promethean.  The sin-eater recognizes the promethean, and starts an unusual relationship. 

   Are you going to have the sin-eater affected by disquiet?