''Space-Time.''

"You shouldn't get carried away like that, you know?" It was surprisingly Lanya who raised her voice whilst drinking her tea.

Arima's eyes dilated and his Silver Emperor's aura was retrieved. He then smiled wryly. He had always lived a life of battle and was used to it to the point he would need a fight every now and then. At the thought of a worthy challenge, he got a bit too excited. He was aware of that.

But he never expected Lanya to be the one preaching him. She was usually reserved but thanks to that, her understanding of Arima was pretty high. Maybe it was more because of the awkwardness he felt that Arima calmed down instantly.

He faked a cough and stood up. "My bad…" He said and headed toward the Inn's exit. It was soon time for the lessons to start.

Lanya was amused by his rare uneasy behavior and went after him followed by everyone else.

******************************************

Later in the morning, Night quickly introduced himself to the class as Karma did before. He uncaringly revealed that he was Arima's soul beast and shocked the students. They always thought that soul beasts couldn't take human form. The 'beast' in soul beast wasn't there for nothing after all.

Well, if they knew Karma was originally a weapon, these poor children would've probably become paranoiac, wondering if Lanya wasn't some sort of unknown creature as well.

"Anyway, today I'll try to expound Death, Life, and Time magic in one go. Of course, the last one is a bit more complicated, but it doesn't mean it will take hours to explain."

"First, I'll do Death and Life magic at the same time. Obviously, there's no such thing as an explanation for what is death and what is life. We only know one thing; life endures as long as you're alive while death represents its endpoint."

"If you want to master these two magics, you need to comprehend life and death and everything related to it." Arima turned toward Balan, "Tell me, what did you do to master life magic?"

Balan pondered for a moment and then smiled. "From the moment I was born, my mother worked hard to teach me about life, about the world. She always told me that life could be sad and painful but that there would always be happiness at the end of the road."

"That's why I wanted to learn life magic. After my mother passed away, I decided to become a healer. For that, I tried to learn everything about medicine and biology. I also accepted rescue missions and asked people to tell me their stories to understand my mother's teachings better," He said and Arima nodded in satisfaction.

"There you go. For life and death magic, this is what you need. You need to learn about either one of them actually."

"Life is a tortuous path that you're forced to take, but from which you must never stray away."

"Death is different. It's the end of the road. Most people are scared of it. But it isn't something that should be feared but accepted."

"Without death, life is nothing. You should be grateful even. Men designed the word 'life' because they had created the word 'death'."

"In the first place, nobody knows what is to be dead. How can we keep being scared of something that has never even happened to us? Fear of the unknown? We experience that during our whole life, what's the point of overthinking it once you reach the endpoint?"

"Even undead monsters, reincarnated people, or even resurrected people. They can't tell what is death. As long as someone can stand in front of you and hold a conversation, he is not dead."

"Death isn't something so trivial. It's when you completely disappear from existence. Absolutely no one can say that they 'experienced' death simply because if it was true, he would not be there to tell it. No matter if we're in a world of magic or not, death is death. A zombie, a vampire, a ghost, whatever you want, they are not dead. It always has been impossible to know what comes after true death because it's a one-way road. Even Hell or Heaven, those are just insignificant places you go after your soul leaves your dead corpse, nothing more," Arima paused and smiled.

"Death and Life magic come together every time. One cannot exist without the other, that's a fact. But most people can't master both because the two need a completely different state of mind."

"There is a straightforward method to understand these two ideas. You just need to go upfront and look into it. Only those with experience gained from life and death struggles can really understand everything."

"But there are different opinions everywhere. Everyone understands it in their own way. One can easily become someone who lives to save people or someone who lives to kill others," Arima added and everyone listened to him quietly.

They even hesitated to breathe so that they were sure there was no noise over their teacher's voice. That's how awe-inspiring his speeches were.

"Now, for the practical uses. First of all, there are two things which you can manipulate with Life magic; life energy and life force. The former fundamentally represents your health while the latter is the strength of your soul and body combined. It is possible to interact with them with Life magic to bring changes to the human body. For example, you could heal someone or even rejuvenate him."

"Then, there's death energy. It's an energy contained in undead creatures and it's not weaker than its counterpart, life energy. Never make that assumption. Let's say, if life energy is a positive number then death energy is a negative one. Incidentally, undead also have life force since they have a soul."

"With this said, we can continue. With life magic, you can directly influence mana, organs, and even mental state by combining Mind magic. You can also indirectly interact with the soul through life force. Life magic can be used as a mean to attack by disturbing the life energy in the opponent's body. You can also create things such as blessings if you use it with Light magic theory."

"As for Death magic, this one is a lot deadlier in comparison. If you use Death magic to invade a person's life energy or life force, he would undoubtedly die if he isn't resilient enough. You can also practice necromancy with this magic and raise the dead. But keep in mind that it isn't resurrection at all."

"When you turn a corpse into an undead, it comes back as an entity full of death energy, like a newborn with a new soul. They can then evolve and become intelligent and powerful beings such as liches. Additionally, if you want to 'heal' or 'repair' something that is dead, you use Death magic instead of Life magic. "

"Finally, with Dark magic theory, you can make things like curses and plagues. A really dangerous thing," Arima smirked and his students smiled wryly.

"Magic relies a lot on your mentality, and those these two magics are particularly affected by it. To finish this topic, I want to tell you something. The most significant key to master magic," Arima declared and his students' eyes flashed with interest.

"It's very meek actually. 'Broad mindedness'," He uttered and the students showed a confused expression.

"That means you need to be open-minded under any circumstances. You always must be able to accept anything that comes at you, you should even consider that anything can exist."

"To be a true mage," Arima paused. "You must think of imaginary as a reality. Nothing is impossible and nothing is irrational. Everything you can think of is authentic and real," He said and his students fell into deep thought.

"To be honest with you, in this respect, I have the arrogance to affirm that you won't find better than me," Arima smiled. "In any case, this is my advice. Keep your mind open to anything. This is far more important than it sounds. It allows you to see authenticity behind fallacious and lies behind the truth. Heed my words, children. This is genuinely the thing that enables humans to soar to new heights," He stated and his students nodded frantically.

"Good. Now, you all know about the last one, right? The hardest magic to master amongst the non-elemental category, Time magic."

"For starters, let's try to express what is time. Firstly, I need to clarify something. Time isn't something 'out of this world' or an unknown power which affects the world. Look," Arima pointed toward the ceiling and a projection appeared.

Red squares started to appear here and there in the classroom. "Those red squares are the matter in our world," He said and everyone acknowledged it in their heads.

After that, within the red squares and around them, blue spheres popped out. "You already know what this is, 'space particles'. Lastly," Arima waved his hand and a new element was added to the hologram which occupied the whole ceiling of the room.

This time, countless white thin lines suddenly covered matter and space. Those white lines were constantly moving toward a single direction like a stream of water.

"This is what we call time," Arima declared and his students exclaimed in surprise.

"Yes, time is actually similar to space. It's not something really mystic or ethereal. To explain it to you in the crudest way possible, time is a sort of energy omnipresent in the universe which acts as what we call time. It will make the molecules and atoms move so that we get older, so that objects decompose, water flows, light travels, etc…"

"That's why gravitational fields can actually disturb time. I'm sure you don't know what I'm talking about, so look at this," Arima pointed one more time pointed at the projection.

Among the numerous white lines, a green circle emerged. "That green point is a planet," Arima commented. "Now observed the lines," He instructed and his students looked closely. Then, they noticed that there was a slight change in the speed and trajectory of the white lines around the planet.

"Every planet or star emits a gravitational field. The slight disturbance you're seeing on time is caused by the field. Basically, it means that gravity can affect time, proving that it isn't something elusive."

"For example, if I happened to carefully create a gravitational field strong enough around the school then the time within the school will be slower than outside to some extent," Arima explained and the students were mind blown.

Even Arister and Lanya widened their eyes. Only Karma and Night were unmoved. The two of them were connected to Arima, so they more or less knew the same theories as him, even if they weren't very clear about it.

"One more thing, from where I come from, a renowned man named Albert Einstein proposed a Space-Time theory. First of all, you have to consider that space and time fuse together to create a sort of relative platform."

He said and the projection cleared before displaying something else. It was a planet hovering above a sort of blue grid, or maybe it was more accurate to call it a net. That net seemed to be dug by the planet itself, creating a hemispherical hole

"That net is Space-Time, depicted as a two-dimensional surface. The hole you're seeing in the middle is created by the gravitational field of the planet. This brings me back to the question I raised previously; where does gravity come from? Well, it's weight. Something heavy placed on the Space-Time will naturally deform it and that's what we call gravity. So, the heavier something, the more gravity it generates."

"Back to our main subject now. On this representation you're seeing right now, the time at the bottom of the circular cavity caused by the planet is different than what it is outside of it, farther from the planet. That's why two people, at different places, can measure a difference in relative time compared to the other."

"Well, that's more or less what I already explained, we call that time dilation. I will pass all of the details and explanations about Relativistic Time for now and skip to the 'world line', also thought by Einstein."

"That theory says that we should not be considering time like it is 'flowing' or 'passing'. Based on that theory, past, present, and future are all mingled together at any specific point in space."

"The past is not something that happened once, it's something that is there. Time is like a higher dimension in which we are compelled to travel in. There's actually no relation between past, present, and future. These three terms were only created for, let's say, the common people to understand."

"But it's actually just an 'illusion'. Things that you experienced, that you qualify of past, are actually still there in the Space-Time surface, you just can't reach it. Same with the future. As for the present, it's nothing more than your current location in the Space-Time dimension."

As Arima continued to speak, everyone's thought process started to fume. "For example, if you happen to travel in time somehow one day, you won't actually travel from present to the future or the past. You will just be able to escape time's overwhelming control and go against the flow to relocate yourself on the Space-Time surface to actually go somewhere else, which is the past or the future."

Arima said and sighed lightly. He looked at his students and smiled. "Of course, all of this was simplified. Even I cannot make it any simpler without saying some senseless things. The way I explained it to you already would definitely be criticized by scientists if they had heard it," He said and his audience's mood became quite depressed.

They already had a hard time understanding their teacher's abridged explanations, they couldn't even imagine how complex the entire thing was.

Arima chuckled. "If you want me to explain the details of this, ask me later. I'll do what I can to clarify it," He announced then smirked. "But, it's not over," He added and his students trembled. They gazed at him incredulously and hoped he was joking.

"If this was enough to use Time magic, then the gods would have already mastered it for ages. From my understanding, there are two reasons why most people can't achieve positive results with Time magic," Arima raised two fingers and smiled.