Cam is dipping a grilled cheese sandwich into a bowl of tomato soup when he feels the summons. He goes ahead and grabs it. Doesn't even drop the sandwich.
"You're certain that this is blood? It's absolutely tasteless."
"Yep, it's blood, but it's from a person who doesn't exist. They could've, but do not. Okay, I'll try some of what would have been mine back when I ran on biology." He makes another, matching teacup, puts a dram of blood in that one too, and offers it, crossing his fingers.
"Equally tasteless. It's odd: animal blood is violently repellent to vampires. Human blood tastes vaguely sweet, with variations by person. This... is neither."
"Okay. ...I'm going to give you a quantity of blood belonging to a real person who is dead who has spent no time as a daeva. But they were a total jerk so I don't mind mildly inconveniencing them for science." One teacup of Hitler blood.
"Could it be that created blood doesn't work for some reason?"
"Yeah, looks like it. There goes the cunning application of demonic power to the problem of blood supply. Damn."
"Perhaps it's somehow related to the fact that if you feed off someone until they go catatonic, you stop being able to draw sustenance from them, even if they still have blood left. I haven't done this experiment myself for obvious reasons, but I have confirmation from multiple vaguely trustworthy sources."
"I could try a live person." Cup of the blood of an asshole serial killer currently imprisoned on the Moon?
"No, still nothing."
"Okay, I'm out of ideas for categories of demonically created blood. I guess I could do angel or fairy but I can't think of a principled reason for them to be different from demon blood." Cam picks up his device again. The reflection of their surroundings winks out. A few lines of text in a language Isabella won't recognize appear in its place, and then they too disappear.
"... There is one more thing we could try, from a scientific perspective. Would you be willing to let me bite you? It could be that it's blood from people from your world that doesn't work."
"I mean, if that's your hypothesis, name someone from here and I'll make a cup of their blood," suggests Cam. "Biting me won't scale unless I turn out to be totally immune to the side effects and want to spend most of my time getting bit."
"Well, my blood's out for obvious reasons, and I don't know of anyone who I both dislike and isn't a vampire. I suppose one of my human servants will have to do. Sophia Leanne is next in the rotation."
"These people are cool with it?"
"I wouldn't say they're enthusiastic about it, but they accept it as part of their duties. It's a much better option for them than most any other they might encounter in Shadescast."
"That's not exactly a signed consent form, and I assume none of your servants are literally Hitler."
"Would you prefer for me to starve to death, or to have to concentrate my feedings such that they would permanently harm those I fed upon? I have to maintain a certain number of servants in order to limit exposure, and those who would willingly be fed upon out of the goodness of their hearts are few and far between. The current arrangement is not ideal, but it is acceptable to all parties."
Cam peers at her assessingly. He sighs and makes a teacup of the named person's blood.
"It appears that we've determined that created blood doesn't work."
"Yes. I would love to never have to bite anyone ever again. And while we're wishing, I would also like to not spontaneously combust in daylight."
"How does that one work?"
"If I go outdoors on a bright, sunny day, I spontaneously catch on fire wherever the light touches me, regardless of how many layers of clothing I'm wearing. If I go out on an overcast day or towards twilight, that can be safe, but if have to watch the sky carefully and keep a tight hold on my parasol."
"Sunscreen? Ultraviolet light alone?" inquires Cam.
"I don't get peeling, irritated skin, I ignite. Sunscreen doesn't help. What's ultraviolet?"