BloodRayne/WMG

Severin is a ghost.

 * He's staunchly non-combatant, but no ethical or practical reason is given.
 * He's good at getting information on Rayne's current situation.
 * He can safely get into and out of places that would be dangerous for humans, even non-affiliated vampires/dhampirs.
 * He only ever appears when Rayne is otherwise alone, sometimes immediately after anyone else has left, and vanishes before anyone else appears.
 * Severin and Rayne never touch. This is thinly circumstantial evidence, though.
 * Circumstantial counter-evidence: Severin is seen sitting in the driver's seat in his introductory cinematic. He's not seen holding the wheel or operating the vehicle, but it sounds like the door opens and closes when he leaves.
 * Here's where the trees get admittedly more epileptic: Ephemera only speaks of Severin in the past tense. She may or may not know that Rayne is still in communication with him. And Severin's encouragement sounded a bit vindictive with regard to Ephemera.
 * Ephemera doesn't speak of Severin in past tense. "And how is our dear Mr. Severin? I made sure he dreams of me every night." He is implied to be a black shadow thief who was "stolen" by Rayne just before Ephemera transformed him.
 * If Severin is really coming in over a radio as it sounds like, why doesn't the necessary hardware ever appear in her ear, either in-game or cinematic models?
 * It didn't for Rayne either.