Instinct: Ookami no Ichizoku

Even though the mafia is known in present day as the rulers of the underground society, the origins of the organization spans ages ago during a time when they were the protectors of refugees that even the police disregarded. This secret society was divided into two families: the Gustav family and the Vito family.

Gil is the youngest of the Gustav family who are all werewolves. He is brutally honest, smart and loyal, but is incomplete, as in he cannot fully turn into a werewolf. He keeps himself out of the family business and spends his time with the common folks. But when the vampire Vito family starts an all out war with the Gustavs, Gil has to step up to the plate and show that he is capable of leading a mafia family.

(Source: MangaHelpers)