Alchemist said
"How can I help you, you asked. Well I've a theory...." Eren started to explain "every thing in this world is comprised of Aura. Whether it's the rocks, plants, air, animals, or even a person, They all have a distinct Aura. We call this an Aura Signature and we Aura tamers can see them. It's like the world lights up with all new colors." Eren then started to explain "My ability to heal and regenerate is where thing get important... You see, I have to absorb the Aura of something else and transfer it's essence in order to regenerate or heal someone else. I generaly take this essence or life force from plants and inanimate objects but in theory, I could drain the essence of a human and watch them wither away." Eren finished explaining and said " I believe that this might work on a Vampire like you also and that would explain how I can help."
"Are you offering to drain a vampire lord for me?" Roxy asked in disbelief. She had never thought of something that crazy. "How would you even get close enough? Why would you even want to do that?"