Sevis is the oldest of Raoul and Emma's children and has always been something of the favorite. Unfortunately, this fact, coupled with his lineage, has led him to being more than merely spoiled, he's a full-blown sadistic psychopath. Reinforcement was problematic in a household where torturing your siblings is a family game and he has experienced nothing in his life to suggest to him that the world doesn't revolve around him and his desires. His mother noted his tendencies and decided to kill two birds with one stone. In order to keep control over him and because she needed an agent in New Orleans, she ghouled her eldest and sent him forth.
As expected, the lust for blood has kept him manageable and he's doing a fine job of coordinating with the Serpents to establish a firmer control over the drug trade and get more potent narcotics on the streets. His drug dealing is motivated more by his sheer sadistic desire to torture people with their own appetites as service to his mother and so she's had no trouble with him. He may, however, get distrated at some point and chafe at the blood bond keeping him in check. Because of this, Emma's asked Beranger and Joseph to keep an eye on him, a fact which he has become aware of and is deeply unhappy about. Ironically, this more than anything may lead to him testing the strength and length of his leash.
Sevis is utterly self-absorbed, to the level of being sociopathic. Incapable of comprehending the emotions of others, he is still very adept at manipulating them, as any true psychopath is. His disregard is played off as a charming roguishness, helped by his good looks and copious cash, and he is seen as something of a party boy by the rich young folks he gets hooked on crack and XTC.
In reality, Sevis is a vicious little cuss who will kill someone who irritates him or sit and watch a client go through hours of painful withdrawl for the pleasure of it. Easily bored, he is constantly searching out new distractions and fun ways to amuse himself, leading to a lot of carousing, purchasing of expensive toys, and other petty indulgences. His excess has put off the more professional drug dealers in town, particularly the non-Cathari Serpents and the Lasombra, who are smugly waiting for the revenant to crash and burn.
Sevis's derangements don't lend themselves to deep relationships and his solipsistic self-involvement prevent any real affection for anyone but himself. His loyalty to his mother is based almost entirely on the blood bond and whatever family loyalty he may have felt has been lost because of distance and the perceived 'betrayel' of Uncle Joseph and Great-Uncle Beranger.
He does, however, get along well with Ange Poncelet, whom he's taking particular delight in watching deteriorate. The other Cathari are cool towards him, just because he's so self-absorbed as to be a detriment to the sect in many opinions, but they still deal with him. As mentioned prior, the Lasombra and non-Cathari Serpents won't do business with him at all and take particular delight in any trouble he gets himself into, citing it as a failing of the philosophy.
Most of Sevis' power in the city comes from his control over his high profile clients, most of whom will do whatever he asks on the threat of having their supply cut off. He's done a passable job of causing much of his competition to go missing, so there aren't a lot of options, but should the Serpents decide to move in on him, this won't last long.