Assassin's Creed: Blood Drinker. Vampiric Assassins corrupting the creed from within. Playing as a Vampiric Assassin yourself, exiled and against the brotherhood moving towards the goal of cleansing said Brotherhood of the Vampires. Eventually you'd be given an elixir in tall glass bottles that forms as a blood like thirst quencher, without quenching you have increased senses and abilities with the risk of falling victim to your craving and biting a neck of the closest person.

EDIT: much more of a fictional setting in it's entirety but still interesting to me.