Magic

"Six? The fuck are you doing here?"

"Well, Lilin, your duties cannot wait for an explanation thorough enough for Ten here, no? You should tend to them before the King grows wroth with you."

"I-I... Uh... Fuck, whatever. Tell her whatever, but if the King gets on my ass about it, you gotta explain."
Lilin tossed a hand into the air in a dismissive gesture as she spoke, then she turned and left in a hurry. Annie could see the restrained anger, glad that Lilin was holding herself back for her sake.

"Now, Ten," Six said, "allow me to explain what a person's Core is properly."

Annie nodded, mentally preparing for a massive dump of information. It'd been a long while since she had been to school, but hoped she would remember how to remember things.

"A person's Core is a sort of... Mana-based organ within their body. Similar to a person's heart or lungs, it is critical to their functionality, but it isn't a physical form within them. Instead, it's a point at which Mana is most concentrated within a person's body. However, this Mana density means it takes on special properties. The form the Mana takes is based on a person's predilections. The most common Core types in humans are Life, Fire, and Wind. Demons have different Core types, though that might not be as important for you to learn."

Annie nodded, trying to wrap her head around the various terms being thrown around.
"Uh, do you know what type I am?" she asked, though she already had a good guess.

"Typically, I would be able to tell you at a glance. However, you appear to have an anomaly about you, as you don't have much of any Mana flowing in or out of your Core. Typically, that is a sign of excellent Mana control, but that is only the case when it comes to trained magic specialists. In your case, it may indicate an abnormal condition."

"Condition?" Annie asked. "Like what?"

"Well," Six said, adjusting her glasses, "I can't be certain, but I believe that you may have a Mana Processing Deficiency."

Annie nodded, only to realize Six had stopped talking as if that meant something important. "Uhm... I'm not certain I know what that means," Annie said uncertainly.

Six nodded, her expression unreadable as she continued. "That means that any Mana taken from your Core will be extremely hard to replace or replenish."

"And... That is bad, because...?"
Annie wasn't usually bad at puzzling things together, but being able to ask these questions to know for certain wasn't an opportunity she wanted to pass up.

"Because if your Core is ever emptied of Mana, you will die."

Well that certainly was easy to figure out the consequences of. Annie felt her gut wrench as she realized the implications of that. Each time she healed somebody, she was using up a permanent resource.

"I-I see," Annie said, "So, does that mean that I can't really use magic?"

Six adjusted her glasses again, pausing before replying. "Give me your hand."

Annie hesitated, unsure of Six's intentions, but slowly reached her hand out. Six took hold of Annie's hand, then closed her eyes. A flash of pain went through Annie's arm and into her chest, but it was gone as fast as it had appeared. Annie didn't even have time to flinch before the pain was gone, leaving her questioning how intense the pain had even been.

"Yes," Six said. "You will be almost entirely unable to use magic."

Well that was a bummer.
"Why's that?" Annie replied, "and what did you have to check to confirm that?"

Six let go of Annie's hand to explain.
"You have a Life Core. This is the most common type of Core among humans. However, it is also the least useful. Life Cores have the benefit of allowing a person to heal somebody without learning Mana Conversion, but it also means that they are practically unable to use Core Conversion. In order to use magic, a Life Core mage would need to do almost everything through Direct Conversion, which takes a great deal of training. The only other option would be to draw from their Core- a luxury you do not have."

"Oh, so all I would need to do is learn this Direct Conversion to use magic?" Annie asked.

Six shook her head. "Not exactly," she replied as she adjusted her glasses again, "because you also lack experience with Mana in general. A person who had been taught of basic Mana principles as a child would not ask me so many questions, so I believe you would need to be taught as a child would. Unfortunately, that usually requires teaching Core Conversion. In your case, there are no environments suitable for teaching you Core Conversion with your Life Core. Thusly, you would need years upon years of teaching and studying to be able to use any magic other than your Core type. As a servant under the Demon King, you have no need for such intensive training, and thusly you will never learn magic."

Annie frowned. She had really, really been looking forward to learning magic. Hearing that she couldn't learn it was fueling her to learn it, but there were so many uncertainties. She wanted to ask questions, but didn't really know what to ask. It was frustrating.

"What happens if I do use my Core?" Annie asked.

"Well, beyond simply killing you if your Core is depleted, you will likely experience serious physical symptoms as your Mana levels run lower. It's impossible to know for sure how your body will react, but a common reaction is to grow progressively more ill."

"So... You think that if I use my mana, I'll get more and more sick?" Annie asked.

"It's possible," Six said, "but I don't believe that that is the case. If it were, you'd likely already feel slightly ill from your Core's natural drain. I can't be certain as to what your reaction will be, unfortunately."

Annie nodded glumly, curious about what her side effect would look like but now submitting to the idea that she won't be able to use magic much at all in this world. It was a tough pill to swallow, but at least she still had her youth! Not to mention, an answer to why Lilin was so against her using her Core. Annie smiled a bit now, the thought of Lilin protecting her twice in one day reminding her that there is still hope of changing Lilin for the better.

"Alright, thank you dear," Annie replied. "You've been so kind to me, how could I repay you?"

Six paused, but her expression didn't break. If she was surprised or confused or shocked, she didn't make it known. She simply pondered, and then she spoke.
"The biggest kindness you could do me is simply keep yourself in good health and good standing with Lilin. There are many duties to handle, and having another pair of hands working is easing all of our minds."

"Oh! Well, I'll do my best, dear. Now... Where would Lilin be, do you know?"

Six sent a pulse of magic out, Annie noticing the feeling of energy rushing past her. It was like a warm breeze, only it didn't mess up her hair. Then Six replied:
"She will be in the kitchen."

Annie smiled again. Even if she couldn't use it, magic was such a neat thing! It really did feel like all those stories and shows that had magicians and such.
"Thank you, dear! I hope to see you again!"

With that, Annie took her leave and Six let out a soft breath of relief. Ten was wonderful company, and that kindhearted nature made her nervous of what may happen to her. She just hoped she and Lilin would continue being there for one another.