This probably wasn't the best time to have a wandering mind.
He should be focusing on following the younger sister of his now dead sparring partner into a bandit camp inside a Dungeon, who was determined to kill them all under the assumption they were cultists who targeted her brother.
But instead he was thinking about magic.
It's been about five years since he was able to use it himself, so his personal experience could be compared to a textbook with some knowledge.
Magic was weird. Or rather, the history and explanations of what people called 'magic' couldn't be summarized in a few months of lectures from Zenith and a few books.
Especially not when those books contradicted each other, and were published decades apart.
The fundamentals of magic had yet to be simplified for a beginners course, instead it was still a field of study that mages were encouraged to go into.
For the longest time, the basic name for magical energy had been Aether, and when it became clear that different elemental energy existed, they developed the word Mana to refer to them after specifying the elements.
And so it was believed that to cast a Fire spell, one would need Aether and Fire Mana. But as more mages studied magical energy, they made discoveries that contrasted each other.
Generations of research couldn't unravel everything, as each new theory would set acceptable explanations back a few decades, and only rarely did they advance.
The general foundations of magic were set in place a few hundred years ago.
It was commonly accepted that magical energy existed as tiny base particles with special properties, some called them atoms or pure essence, that were susceptible to influence by the thoughts of sentient beings.
And when the base particles combine with other particles corresponding to the fundamental elements (fire, earth, wind, and water), and the forces of attraction and repulsion acted upon them, then that was how Manacules (small mana) took shape and magic took form.
Of course, this level of magical theory couldn't be taught to a magical inclined child or to the ignorant public, so as far as the uninformed were concerned. Mages and magic catalysts had Mana, which was used for magic.
And the books for beginner mages used dual termed combinations of hot, cold, wet and dry, when instructing mages to influence their magical essence to take on elemental properties.
Overall, if Rudeus wasn't trying to become a mage, he would've never read any books on magical theory.
Anyway, his mind had wandered for a reason.
In the past, mages had discovered a similar magical energy to 'aether', and Manacules, inside lesser, more corrupt beings.
Within the beings called monsters, the magical energy they generated was a corrosive sort that corrupted other things after prolonged contact. Mors, was what mages called it.
And just by their existence, the Mors drifting off of them infected the Mana within the air and changed it to something else, Morscules.
As organic and inorganic matter was exposed to Morscules for an extended period of time, they changed in ways not yet completely understood.
Most living beings would die, some fauna and flora would become magical beasts and plants. Water became poisonous and stale, soil became inept and minerals would either crumble or transform.
Morscules in their raw state could only be influenced by monsters and their desires, so the transformation of the terrain was pretty standard and without much variation. And the fact that certain subraces of Demons could use Mors and Morscules was enough for them to be labeled as monsters.
Caves became monster nests and hunting grounds, and soon they became known as Dungeons.
Rudeus understood what exactly had caused him to feel odd when he entered this Dungeon, the Mana drifting off his skin was being pressed against him from all sides.
The pressure of Morscules was swarming him and attempting to corrupt his Mana, so if he didn't keep a conscious awareness of it, he would lose command over it.
Unfortunately, he hadn't found many books that focused on Dungeon diving, but he had seen an excerpt that had confused him until now. Apparently, inside deep Dungeons or Labyrinths, most low level Adventurers went mad and died.
'I know this world is a bit odd, but most of the things I could understand as common isekai things, however this world's magic and dungeons were just confusing.'
He was LV0, and he was pretty sure it was only because of his large Mana Capacity that he wasn't being corrupted. In all the books he had read, there existed no defense against Morscules, a person could only resist it with willpower or Mana.
Speaking of his Mana, when he had learned to feel and sense it, at first he had imagined a large sphere as his container for it, but that changed after a while.
The more he read and remembered how Zenith described it, his image began to change into a silhouette of his body that contained his magical energy.
It wasn't just an imaginary change either, the next time he tried a spell, he could feel his Mana directly leaving his silhouette and his skin simultaneously.
Further reading had changed them into thin pathways within his silhouette, the ease at which Mana left his body changed slightly. It had become clear to him that he wasn't learning how they were, but rather how he should mold them.
He understood why the books were guiding him to create thin paths, as the Mana contained inside were concentrated, therefore increasing the effects of a spell, and they gained some additional pressure when firing off.
Still, he had modern knowledge of multiple fantasy worlds and their magic systems, so he had felt confident that he could probably develop his own internal network.
Experimenting around, he didn't really get anywhere or discovered anything groundbreaking. And in the end, he basically molded his magical network into how the book described it.
The only real thing he added on the design was a heart-like core, lung-like system, liver/kidney-like filters, and vein-like paths. Pumping, cleaning, and circulating his magical energy was the limit to his creativity.
He wasn't an engineer, physicist, programmer, biologist, nor an architect. He had no idea how to construct an engine, reactor, computer, nor any system for fluid, heat, or electrical transfer.
The only other thing he did that wasn't in the book, was move his central point/gate —the origin of newly generated Mana— into his brain. So the influence from his thoughts on his magical energy was a bit faster.
As time passed with that form, he noticed that it was growing harder to change it as it solidified in his mind and body with that shape.
Even with his Mana Veins circulating it, his control wasn't good enough to stop every but of it from drifting off his body, and when he accidentally became keenly aware of it as he casted a spell, he learned about miscasts and shaping Mana outside his body.
When he attempted spells now, he first emitted a bit of Mana in the loose shape he intended, he could mostly just manage spears, loose lines and other basic shapes.
As the unconscious portion of Mana left his skin and out of range from his control, he always made the effort to cut off any connection to avoid an unintended miscasts.
But inside this Dungeon, his drifting magical energy was being forced against his skin, and with every breath he was inhaling it and some Morscules.
The filters he created were now being out of use as they rejected the foreign magical energy from settling in his body.
His mind was busy keeping track of his own Mana, and his body was taxed with trying to stay clean.
However, Daisy wasn't a mage, so it was unlikely that she had his defenses, and yet her footsteps deeper into the Dungeon didn't falter.
Rudeus risked his life by getting closer to the girl on a murder mission, and he felt the Morscules around her being burnt up.
He didn't understand it, but the book had mentioned willpower being another way to resist.
'People can't use it, but maybe the residue from the Mana that had been corrupted can still be influenced by people and their thoughts can cause it to break down. That is the only explanation I can imagine. Still, it probably takes a tremendous amount of determination to overwhelm it.'
In the year he had known Daisy, she didn't leave much of an impression of herself on him, and what little she did wasn't positive. She was a small girl with a nasty glare.
Luke had said she wanted to be an Alchemist, and she did read books and collect streetside herbs, but she didn't have any passion.
One day, when his sparring partner had caught a cold, and she had come to inform, he offered to teach what he knew about alchemy. Of course he didn't know much, but he did know the basics of chemistry and cooking, as well as what he picked from isekai books.
She didn't even seem tempted in the least, and without a single blink, she declined.
When Monica, the waitress at the bar part of his home and self-declared guardian, was free she mostly watched him train. And that included the spars, she was mostly off on the sidelines cheering for him, and next to her was a quiet Daisy watching her brother.
Every time Rudeus would draw blood or leave a bruise, he could swear she glared at him. Every time Luke would win a match, her expression didn't change.
After they were done sparring, Monica would hand out lunch to everyone. She said it was a thank you gift to the siblings.
Even though he himself didn't feel that close to Monica, Luke had treated her like an older sister he respected, but Daisy didn't show any sign of appreciation for the free meal.
One day, when Monica offered to help Daisy set up a small garden in the clearing, she refused. Simply stating that she could gather what she needed from around town.
If she wasn't so immature, then Rudeus would've thought she was the reincarnation of an anti-social soul. The possibility wasn't completely ignored, but since she didn't carry herself like a teen or adult, he dismissed it.
Even though he was the one carrying a lantern, stolen from the corpse of a 'cultist', Daisy was still the one leading. Her pace was just barely kept within the light's reach.
He didn't know what he should be doing right now, so he focused on his Mana.
Even though she was a small girl, younger than his body by a year, she possessed a terrifying aura and a demonic murderous intent.
'With just two daggers and a surprise attack, this 8yr girl had killed a LV80 Assassin. Even if she had stabbed through the eyes and into the brain, they had 310 HP, and she had killed him. Or wait, technically I just saw him lying down bleeding before I shot a spell into his skull, so maybe I dealt the final blow.'
The fact that he had killed somebody had yet to cause a change to his thoughts or emotions, it was just his own near-death experience and losing out on his sparring partner that caused him any grief.
Still, Luke was technically a distraction, so now he will be able to focus on his magic training again.
His own thoughts were brought to a halt as he turned a corner and saw a distant room lit up by its own light source.
"Stop." Almost immediately he whispered and his free hand shot out to grab a young girl about to rush off. He placed the lantern down around the corner, and turned his attention to Daisy.
He focused, since he was whispering the guidance of Mana within his body needed some support since he was using spells he wasn't too good at yet.
"Hear my plea, o' God's who graciously watch over all who hunt, I ask of you to bestow a blessing with the speed of a tempest wind onto the soul before me, Haste."
He wasn't too familiar with support magic, so he had yet to truncate the incantation or find any alternative words.
Even with a cloak over her body, the effect of the spell was clearly visible as her impatient twitching doubled in speed.
"Hear my plea, o' God's who graciously watch over all who clash, I ask of you to bestow a blessing with the might of an iron mountain onto the soul before me, Power."
As her strength doubled she tore away from his hold and silently shot off.
With one more use of Haste, on himself, he followed after her.
By the time he crossed the doorway into the room, he saw a beheaded corpse on the ground and a small cloaked figure fighting against a swordsmen.
The man wasn't clean shaven and his skin was marked with filth, so the odds are he was a bandit. Or just an unhygienic Adventurer. He seemed to have some struggle against Daisy, but not one for his life, but rather a struggle to end her life.
A steel sword would sing through the air, narrowly missing a small girl, and occasionally shattering daggers aimed at his heart and neck.
"Assassin! I knew we couldn't trust your lot! I may be a bandit, but I'm not dumb! We were running our operations fine before your benefactor got involved. Also, did you shrink or sumthin?"
The man shouted as he kept missing while defending himself.
Daisy was using her doubled speed and strength to run circles around the man as she attempted to stab him with daggers that kept manifesting in her hands.
'I knew it, she also has a weapon summoning Skill. Also, by the looks of it, if I didn't buff her, she'd be dead. More importantly, that guy is yapping too much, I can't let him reveal who's actually behind hiring those assassins, it's probably a corrupt noble or something.'
"Answer my calls, great earth spirits, I beg of thee for the strike of a mighty stone piercing spear. Earth Spear."
The chant this time was shorter and faster, but it had less power and speed, since he did have to carefully aim it, he thought the trade off was worth it.
When a spear of hardened stone suddenly entered the mix, the swordsman reacted quickly and deflected it. Daisy took the opportunity to stab a thin and long dagger into his eye.
"GAH! You bitch!"
A wild swing of his sword sliced straight through the arm that was holding the dagger. As the young girl staggered after losing a limb near her elbow, the man used his other hand to drive a punch into her face.
The small body in a black cloak crumpled to the ground, and the man raised his sword up high above his head.
"Guhh…gk…"
A spurt of blood spilled out from the hole in his neck. In his enraged state, he had missed another stone spear being fired at him. A hole the size of a fist had been carved into his neck. His throat was ripped open, along with some pretty important veins.
The man's strength, his vitality, his blood, his life was leaving his body. And with the last of his ability, he looked towards where the spell that had killed had been fired.
After firing off his spell, Rudeus hadn't expected the man to remain standing for so long. The dead man turned his head while missing a chunk of his neck, and his unstabbed eye stared down at him from across the room. He was able to see the moment the spark of life was snuffed out.
Fortunately the standing corpse fell backwards, away from the collapsed child.
As Rudeus walked across the room over to her, he clearly heard the sound of rushing feet against the ground. The odd thing was that it had originated from inside the room and was heading away from him.
As he turned around, he spotted various people of different races and ages dressed in rags with shackles running down the path he had come from. There were even some that weren't running, just shivering, flushed against the walls.
'What?'
In his confusion at somehow missing the people in the same room, more of them got up to run away.
'Did I seriously get tunnel vision so bad that I missed a bunch of slaves in this room?'
By the time he had accepted the reality, that he had been so focused on fighting that he missed a room full of people, all of them had run away.
'Well, their rags are a similar shade of gray as the walls, and the lantern in this room isn't too bright.'
Just as he was about to return his attention to the fallen girl, Rudeus noticed something out of the corner of his eye. Not all of them were gone, left behind in the darkest corner was a small girl, sitting still.
If she didn't blink, he might've thought she was a corpse.
He looked around, and didn't find a single other person remaining.
'Daisy's probably knocked out, and bleeding out so I have to be quick. I need to know what happened here before I heal her so that I can twist the truth.'
With that in mind, he approached the girl sitting in the corner.
Smaller than him and Daisy, short black hair, a single dog ear on the right side of her head, and a stump on the left. Dull blue right eye, a scar that covers her left eye, and blood dripped from the corners of her lips.
Sitting curled up in the fetal position, her hands and feet were exposed, and it was clear that she had been de-nailed on each of her limbs.