At Arima's words, the students focused like never before.

"The general and common way to spontaneously strengthen one’s body is with the neutral affinity. You make mana flow through your body. Incidentally, it's easier when you imagine it flowing through your veins as blood does,” Arima declared and at the same time, a blue glow highlighted the veins of the figure projected to illustrate his words

“Though, that depends on the individual. I personally prefer that method but there are people who show better results by using their skin, bones, or muscles. You can even imagine that mana comes out from the brain or the heart then spreads across your entire body. You all should take some time to determine which one works the best for you."

Already at that point, a big part of the students learned something. They had never really thought about that before. Most of them just covered their body with mana instead of using parts of their body to channel it.

"Anyway, once you finish circulating your mana, you can advance to the next step. Look at the projection. The blue glow represents mana, of course, and as you can see, that same glow is fluctuating and is not stable at all. It's sometimes bigger and sometimes thinner. In this situation, the body is not reinforced at all."

"Now, do you know what comes after this?" Arima asked. "It's not a trick question by the way."

"We need to interact with the mana, usually by chanting, to stabilize and manipulate it," Irian answered almost instantly with a loud and clear voice.

Arima chuckled. "As expected from the expert in the domain. At this point, it's similar to magic. Depending on how you imagined it or how efficient your chant is, the strengthening will be either stronger or weaker," he explained and glanced at the projection.

"Let's go with something like this, [Diamond Body]," Arima intoned an example.

Instantly after, the blue glow in the veins of the projected silhouette started expanding and became extremely thick, shrouding the figure itself. But, although it became bigger, it also turned out to be exceptionally stable and every uneven fluctuation had disappeared.

"There you go; the strengthening occurred. But there is a certain characteristic with this one. What do you think it is?"

"The density and quantity of mana used," once again, Irian spoke first. "When you fill your body with that much mana during a strengthening, it means that will be more concentrated on defense as the mana will exert pressure on the flesh from the inside, repelling external damages."

"Correct," Arima nodded. "Now, let's try the opposite, [Bursting Force]," he chanted and the glow considerably shrunk but the intensity escalated. Additionally, it started converging toward the muscles and around the organs.

"That's for explosive strength. It will help the muscles and organs to exert more vigor than normal. Well, that's the base and you all know about it. You can also concentrate your mana in a single point of your body to make it stronger. To finish, if you want to have both defense and attack strengthened at the same time, you have to create different layers of mana and trigger them separately. That would require a lot of mental power though," Arima uttered and the anatomical figure returned to a mana-less state.

"Next, there’s what we call elemental bodies. These have more familiarities with magic, but I still will talk about it today," Arima altered the projection one more time. "Of course, first, you need to circulate mana in your body," he said and the projection moved accordingly.

"Then, the first thing that changes from the previous one is just after. Before chanting anything, you have to integrate an element to the mana. It can be any of the affinities actually, both elemental and non-elemental. So, technically, strengthening your body with space magic is something possible though very complicated."

In fact, Arima used elemental bodies more than once. He strengthened his body several times with time so that he could move in a different time flow than the opponent. He had used it against the Seed of Chaos and Raal.

"For today, I’ll use fire for a demonstration," Arima declared and the blue glow turned into a red one. "You need to be cautious at this point. If you fail to integrate the fire element like it is supposed to be, your body will combust from the inside," he warned and the students resolutely bore in the mind to never try this casually.

"Consequently, you chant something that resonates with the fire element. Something like… [Salamander's Body]," Arima gave an example. The red glow expanded to fully cover the projected silhouette.

"Well, that thing is not really enough to show you," Arima uttered and the sunlight invaded the classroom and the projection dissipated.

Stolen content warning: this content belongs on Royal Road. Report any occurrences.

Arima stood up and the students were a bit surprised. His sigil revolved and he, along with all the people in the room, disappeared.

***

Before they could realize what was happening, the students found themselves on a barren land with nothing to describe on the horizon. They fell into a daze at the sudden change of sight.

They were awakened by Arima's nonchalant voice. "Don't think too much. I teleported you here. Nothing else," he explained them. Although their minds were in a mess because they were not at a level where they could even imagine doing that, they stabilized quickly.

"I just brought you here to give you a real demonstration," Arima said to them and stretched his body, popping the bubbles in his bones’ joints. He then circulated his mana in his whole body and since he talked about fire earlier, he added the corresponding element to it. The temperature in the surroundings increased. Even though it was supposed to happen inside Arima's body, his students felt it clearly.

"[Hephaestus]," Arima used the name of a fire divinity to make his incantation. His body started making cracking noises. His skin slowly turned red like magma rocks. His pupils, irises, and scleras also turned red, with barely any contrast between each.

A black fire started burning at his feet and his skin seemed to be on fire. The students around couldn’t help but take a step back because of the heat.

Arima gazed at them with his red eyes. "This is basically what happens. The main benefit of having an elemental body is to protect you from the same element and also to be able to control it more easily," Arima said and crouched. He placed his hand on the ground and inhaled.

"Like this."

The ground began to melt and blaze before becoming literal lava. After that, Arima still kept standing in the middle of that awful heat as if it was nothing.

"You can also use the basic strengthening technique we talked about earlier at the same time. It's a bit harder to do so, but it's simple once you get used to it," he spoke then released his 'volcanic' form whilst freezing the lava with ice. The abrupt difference in temperature caused a small wind to blow.

"Let's go back," Arima snapped his fingers. They disappeared once again and reappeared in their respective seat at the PA. The students felt like it was all a dream.

Arima once again turned the class into a dark room. "Next, it will be about shapeshifting," he announced and his students visibly staggered at his words.

"Humanoid species have a great advantage. They can transform into something else to gain a stronger body. But as you know, it's actually rarely used. Because it has too many downsides when it is used to reinforce yourself past your natural limits. It doesn't last long, it's dangerous for the body, and can cause serious sequels," Arima revealed the inconveniences of that technique.

"But, actually, I found a way to resolve that problem."

"…" Silence. A silence generated by the shock Arima had just given to his students.

Arima smiled at them. "Let me talk to you about something else before; resonance. When one resonates with a soul beast, he is able to attain a stronger body. In fact, it's more or less the same principle as shapeshifting."

"For example, at the Republic, I fought with someone who completely fused with his soul beast," Arima recalled his fight with Raal. The projection he had made welcomed another figure. It was a massive bull. The human and bull holograms fused together and became a minotaur.

Ofia reacted strongly to that projection. She realized that the person illustrated was Raal, one of the strongest persons she knew. Her brother had once brought her to the Republic and she had encountered him then.

"Well, let's start from there. If we can fuse with our soul beasts, why can't we change our body in the same way? Well, that's because resonance relies on the soul. It's not really the bodies that fuse together, but the souls that join and work together."

"Meanwhile, when you try to shapeshift into another species or race, since you don't know about how the change should happen or the different details you need to take into consideration, it unsurprisingly fails."

"Basically, you can't change into a beast or a monster because you don't have enough understanding of their biology, and you will never understand it because it would need an understanding up the molecular level and further," Arima declared and glanced at the snoozing wolf on his desk.

“For the information, my soul beast here is not actually a wolf. But the process he used to shapeshift is completely different. He had to forcefully compress his flesh and mold his bones, so that made him weaker. Technically, he didn’t become a wolf, he altered his body so that it would look like a wolf. That’s the nuance between shapeshifting for appearance and shapeshifting for strength.”

The students were listening agape. Their thoughts didn’t linger on Night for a long time, instead, they thought about the strange things Arima said; molecules. They didn’t know what it was, but they realized that he was slowly getting this lesson to a conclusion that may shake the entire world.

Arima grinned. "This is the important part. You now understand how resonance works. That's because the soul contains information capable of harmonizing the two bodies. Now, all of you, open your notebooks," he instructed and his students did as they were told.

Arima's sigil glowed and a purple magic circle was drawn on each notebook in the class. It shined with a purple light that pierced through the darkness of the room. The runes were written in many languages, there was some Latin mixed in, but there were also Greek words, runic languages from this world, and even some symbols that seemed to be randomly made up at a first glance.

The students couldn't understand it at all. Even Arister was staring at it with a complexed expression. There were familiar forms such as pentagrams and hexagons but the thing that attracted the eye the most was the well-known Yin Yang symbol in the center.

"This is a circle I created myself. I call it the Soul Contract," Arima said and everyone looked at him.

"Its use is simple. When you kill a beast or a monster, you draw that circle on the corpse. Once you do that, the soul of the creature will directly combine with yours. Then, you will be able to transform your body and make it gain the characteristics of the said creature. For it to work you need to do it in the five minutes ensuing death," he explained.

All of his students were already itching to try it. They couldn't believe something like that actually existed. Especially Ofia. She instantly got an idea and her entire body was trembling with fervor. Her sister appeared to have thought of the same thing as she glanced at her with widened eyes.

"But remember, it's really important; you can only do it once in a lifetime. It's identical to the soul summoning. So, you should choose carefully what kind of characteristics you want before deciding what kind of creature you need to hunt,” Arima sternly warned them.

"If you try to do it a second time, you will either lose control of your body or die. Don't make that mistake, please,” Arima paused and interacted with his projection.

“There's also another use for that circle. In fact, you don't need to kill the target. If you were to meet a sentient beast, you have the possibility to reason with it and convince it, then use this circle to unite your souls. In that case, you would gain a pseudo beast soul."

On the projection, the human figure stood beside a beast. Above their heads, there was a blue sphere representing their souls. The hologram was animated and the figure killed the beast before collecting the soul. The human’s appearance changed afterward and changed into an animal form.

After that, Arima did a reset of the image. In the second scenario, the two figures discussed together and willingly fused their souls.

"Well, you get it,” Arima uttered. “You can try that later. Don’t forget that this technique only works if you don't have already a soul beast. This technique is very useful and powerful, but I admit that it's a lot weaker than an actual soul beast," he added and once again cleared the projection.

"Now, let's talk about the last method. This one is quite special and dangerous, but equally powerful," Arima grinned. "Listen well."