His name is Nero. Those darts are full of his own blood because he's particularly cursed in a way that makes it poison to vampires. This does not mean he is a good person, or even likes other people. He makes the majority of his living off of other vampires who can't openly get rid of rivals for political reasons. Were it lucrative, he wouldn't give a shit about going after other humans. But it's more fun to kill vampires.