Warning! Spoilers for DC vs. Vampires #2 by DC Comics
During his time as the Dark Knight, Batman has strictly abided by his no-kill rule, as the hero refuses to take a villain or opponent's life. However, in DC vs. Vampires #2 by DC Comics, Batman revealed one noteworthy exception to the rule. With the DC Universe overrun by vampires, he informs the Bat-Family they can kill the supernatural beings since they can't be killed and are "already dead."
For better or worse, Batman's no-kill rule has become a defining part of the superhero's mindset towards villains. In his earliest adventures, the Caped Crusader had no problem killing villains. However, he quickly adopted his no-kill rule and has followed that for decades in the comics. The rule has put him in personal conflict with his closest allies. For example, Jason Todd turned into the Red Hood to do what Batman couldn't after the Joker murdered him - which only happened because the hero refused to kill his greatest enemy.
In DC vs. Vampires #2 by James Tynion IV, Matthew Rosenberg, Otto Schmidt, and Tom Napolitano, Batman prepares the Bat-Family to take on vampires. In the previous issue, Andrew Bennett left him a letter warning him that vampires were about to wage war on humanity. After testing the Bat-Family by spiking their drinks with holy water and making them hold a cross to ensure none of them are secretly vampires, Batman reveals his plans. He shows them an impressive gauntlet of weapons and says they won't be taking half-measures in catching the blood-suckers. When Nightwing asks Batman if he's expecting them to kill now, the Dark Knight tells him, "you can't kill them, they're already dead."
Technically, Batman isn't breaking his no-kill rule since, as he puts it, the vampires are already dead. However, by getting the Bat-Family to take down the vampires for good, he's ensuring they can't be brought back to life. So, he's effectively killing the chances heroes like Green Lantern (current vampire enemy number one) have of being restored to their usual selves. It's quite a moral conundrum, but Batman seems very sure of himself.
Batman is making an exception to his no-kill rule due to the insane circumstances around him. With the Green Lantern picking off of the Justice League and potentially infecting other heroes and villains, Batman can't take any risks when it comes to putting down vampires for good - even if he isn't technically killing anyone. DC vs. Vampires #1 is in comic book stores now.
