The next day we had a meeting with Irene, to discuss the joint casting. While we had speculated a bit about potential spells, we needed more information to actually prepare.

We met in a small classroom in the evening. Irene greeted us with a smile. “Good evening students! I have enjoyed watching your progress so far. Joint casting at your age is quite impressive. But what do you actually know about it?”

“Um, not much.” Cassie admitted.

“I thought so. You know how to cast spells. You form the runes in your mind, you turn your mana into the right affinity and you feed the spell. It is relatively straightforward, once you get used to it. The problem is keeping a clear picture of the runes in your head, especially while in battle. The more complex runes take a lot of practice. But a joint casting complicates this even further.”

We all nodded. We had experienced the problems of mixing our mana.

“First, let’s start with reasons for a joint casting. You can achieve something more complex with it. It allows you to combine certain spells and mix elements. It allows you to cast a bigger spell. A joint casting is often used in large conflicts. You can try to shield your forces, or call a storm to hurt the enemy. Joint casting allows a group of senior mages to almost reach archmage levels of spells. But there is a downside.”

I raised my hand.

“Koyuki.”

“You said senior mages. Can’t normal mages perform a joint casting? What about grand mages?” I wondered.

“Ah. A proper joint casting division requires a lot of training. You have to remember, we are the military. We are not sitting in a comfortable room. Our mages need to perform on the battlefield. That means there will be distractions, there might be assassins, or incoming enemy spells. While we teach the theory of joint casting to regular mages, only senior mages qualify for the specialist unit. Grand mages are not common enough to fill a special unit. Neither are archmages.” Irene explained.

“See, proper joint casting requires trust. Mixing mana makes you vulnerable. It would be very easy, even for a weaker mage, to kill you in the process. It’s also horribly inefficient, if the people don’t work well together. Further, there is a limit on how much mana you can use, because the body can’t handle it.”

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Skadi raised her hand.

“Skadi.”

“Why did we get sick during the joint casting?” She asked.

“There are two reasons for that. One, the difference in affinities. As you know, having the wrong mana in your body hurts you. The transformation of the mana has to be handled very carefully during a joint spell. You can damage your ally otherwise. The second reason is that your body rejects foreign mana. It sees it as an attack. A proper joint casting division spends a lot of time exchanging small amounts of mana and training their bodies to accept it. I should also add, that every person's mana is unique. So you have to train specifically with the people you want to cast a spell with.”

I raised my hand.

“Koyuki.”

“Our spells were combined inside the undead, not my body. Was that wrong?” I wondered.

“There are two ways of joint casting. One is with a lead mage as the focal point. In that case, everyone feeds mana into the body of the lead mage. It’s a bad idea to use the wrong affinities like that. The other is combining spells, like you did. You mixed your magic inside your target, the armadillo. Essentially, you cast an ongoing spell that you feed with mana, and then combine the mana for the actual spell you want to cast. It means that the mana, which is still a part of you, mingles with the other mana. There is some strain on your body from the wrong element that way, but it is tolerable.”

“Oh.” Skadi said. “So it’s like when you power a spell with a spell.”

“What?” I asked.

“Skadi is right.” Irene said. “Advanced magic is usually the combination of simpler spells. Normally, you fuel your spell runes with the right mana. But you can fuel a more complex spell rune with spells. Essentially, you need to simultaneously cast different spells in your mind and then combine them by using an advanced spell rune. In a joint casting everyone provides their spell and then someone combines them.”

Huh. I suppose the draugr and lesser vampire were both advanced spells. I had used my mana, but also my friends spells as fuel. In both situations they had been circulating the water or blood. I guess circulating a liquid in a corpse counted as a spell, even if we modelled it after my technique.

“Does this mean we can start learning other advanced spells too?” Helena asked.

At this point we did not even raise our hands anymore. Irene did not seem to care.

“Joint casting is a form of advanced magic. It is simpler because you only need to concentrate on your part, and not form multiple spells in our own mind simultaneously. But it is harder because you need to learn how to accept foreign mana. If you manage a joint casting, it does not mean you will be able to perform all advanced magic. Different spells have different challenges.” Irene explained.

“Are we supposed to cast a spell with the four of us? Or just with two people?” Cassie asked.

“That is up to you. You can form two pairs or do something with the whole group. Or each of you can create an undead with Koyuki, if you want to. I will give you a book with some ideas for simple joint castings.”

That would certainly be helpful. There were a lot of possibilities. Actually, could I cast a joint spell with Nyx?

“In theory, could I cast a joint spell with a tier three undead?” I asked.

“Yes. Of course, there are issues.” Irene pointed out. “A bound undead cannot kill you, so at least you are safe there. But unless there is trust, the spell will likely be rather inefficient. You can command your undead to obey but you cannot command them to truly like or trust you.”

I looked at Nyx, who watched us from her box. I was still unhappy about her eating the headmaster’s pen, but I did trust her. At least when it came to actual combat. Of course, her core was far too small for now. But one day, she might be able to perform a joint casting with me, or even my friends.