Using path of evolution!
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The link is also in the synopsis
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As Yuki was calmly reading through the various requirements of his abilities and the different items they needed to evolve, he noticed that his skills were required to be level 10 before the requirement would appear… and he wasn't sure if he could help other people's abilities evolve or not…
'This trip was truly worth it' thought Yuki while laying on the comfortable bed Leon provided him, before his face suddenly twisted as he felt a stinging pain in his stomach
"Ugh, what's going on…" muttered Yuki, and just as he did, Leon suddenly appeared out of nowhere in front of him and observed him silently as a huge amount of 'magicules' as they called it in this world which was basically mana kept rushing into Yuki's body nonstop and his magic core begin working at maximum speed to absorb them and control them from raging on his body...
"You must have received a strong skill when you were summoned here, which is why your body is consuming this much magicules, otherwise it cannot house the skill… this is the predicament of everyone that gets summoned here" said Leon as he checked Yuki's condition and his face turned serious seeing the terrifying amount of magicules he was absorbing like a bottomless abyss
'Just what kind of skills did this kid acquire… this is already at the level of at least a unique skill' he thought in astonishment but he hid it quite well…
"If this goes on… I feel like I might explode" muttered Yuki through his gritted teeth as he thought 'How come this didn't happen right away… did it require time for my body to adjust to these skills or was it the world that was lagging to act…'
"Try to focus on stabilizing your body, I will summon a spirit to help you control the magicules" said Leon although he wasn't confident even a greater spirit could save him... but Yuki quickly rejected his 'kind' offer 'I ain't letting you put anything in my body you disgusting pervert' thought Yuki before he said "No! go get me as much steel as you have as fast as possible, I have a way to deal with this…"
"Are you sure?" asked Leon doubtfully as he paused his summoning magic and Yuki barely nodded as he used his absolute focus to help regain control of the crazy mana that was trying to overflood his body…
However, suddenly, his balanced magic core begin shining with a white holy light and a dark eerie light and it begin devouring the magicules rampaging through him with and even faster speesd as a notification appeared in front of Yuki
[Congratulations, you have met the requirements and unlocked a new ability of your balanced magic core, Balance!]
[Balance: allows the host to passively control mana and doesn't allow it to become chaotic inside the body and will always keep it at a balanced state!]
'Nice timing!' thought Yuki and he felt that his body that was going to explode from the huge pressure of the mana overflooding it has finally reached a state where he can withstand the pressure slightly, but this was only thanks to his body of stone and undeterred abilities… However, considering the amount of magicules he keeps absorbing, he would soon get overflooded again and go boom if he doesn't take action quickly!
Leon seeing that Yuki was actually capable of regaining control on his own was astonished, but he waved his hand over him and teleported him to one of his warehouses where he stores Steel…
"If you feel like you are about to lose control at any moment, just let me know and I will take action as soon as possible" said Leon as he watched Yuki curiously…
'If this kid can survive through this, he would become a monster' thought Leon...
Yuki nodded at him before he approached a pile of steel and begin devouring it through his path of evolution ability… Yuki watched curiously as the pile of steel transformed into specs of light before it was absorbed into every inch of his body, and in just a few seconds, 10 tons of steel vanished into thin air to Leon's astonishment…
But Yuki didn't stop and went from one pile to another with a happy smile on his face 'Ah how I like free meals'
Leon didn't feel that anything was wrong for now… but he will soon regret not letting this kid in front of him simply explode…
After absorbing 150 tons of steel which were more than half of what Leon had in the warehouse, Yuki's body that kept accumulating light suddenly began shining before it slowly subsided as a new notification appeared in front of him
[Your ability Body of stone has successfully evolved into Body of steel]
'It took more than I expected but I guess this steel isn't 100% pure which is why it took more than needed' thought Yuki with a smile on his face since he could feel his body withstanding the pressure easily now, and it will be a long way until the madly rushing magicules could reach his new limit, so instead they were nourishing his magic core that was absorbing them crazily trying to regain balance...
But despite all of this, Yuki ended up muttering while staring at Leon"This is bad, I might explode if this goes on for long" but different from the expected worried look on his face, he had a wide smile and it brought a shiver down the demon lord's spine
'What's this feeling?' Thought the creeped-out Leon as Yuki approached him and said "Leon, do you have any diamonds? Please, I don't think I can hold on for long…"
'No, don't sell yourself short, I feel like you can probably hold on for far longer than you think' thought Leon before he remembered that this kid was only here because he forcefully summoned him so feeling guilty he said "Yes I do" before he teleported the two of them to another warehouse that was filled to the brim to Yuki's absolute shock
"T-T-this…" Yuki's eyes lit up like never before and he almost begin shooting light from them as he stared at all the shining diamonds…
"Don't be surprised, we are situated near one of the biggest volcanos in the world, it's only natural for us to mine diamonds from it and sell it to other countries… This is in fact one of our biggest traded items…" Leon explained, but Yuki already put him on mute and greedily begin absorbing all the diamonds he could which was the next requirement for his ability body of steel to evolve again…
"You… You shouldn't absorb all of it…" Said Leon whose heart ached watching pile after pile of diamonds disappearing from his vision and started to regret his generosity…
He usually only sells a small number of diamonds to keep their price high, but now he begin regretting not selling all of them as he watched Yuki happily absorbing everything and his hand kept moving back and forth to and from his sword…
Meanwhile, the greedy Yuki kept absorbing the diamonds like an endless abyss while secretly throwing some chunks into his space ring for later use as he thought 'HAHAHAHAHA, I'm rich, suck on that you filthy demons, just wait until I come back and I show you who's boss'
After a while of absorbing, Yuki finally stopped as a new notification appeared in front of him
[Congratulation host, your ability body of steel successfully evolved into body of diamond]
Yuki grinned widely as he felt how no matter how much the mana rushed through his body, it had no effect on him at all!
'I can't even imagine how strong my defense is right now, especially if we add my undeterred ability!' thought Yuki happily before he turned to Leon and noticed that he had a very dark look on his face and couldn't help but ask "Leon, buddy… what's wrong, is everything okay?"
Hearing this, Leon clenched his fists so tightly to the point that even the air around him trembled slightly before he said "WE ARE EVEN NOW!" And waved his hand sending Yuki back to his room in the castle…
'Tch, who told you to keep watching me secretly? You think I would believe that it was a coincidence you quickly discovered my abnormal state, it's obvious you were monitoring me all the time' thought Yuki who easily found a reason to justify himself destroying a huge part of a country's economy selfishly…
'Anyways, my body is still absorbing mana endlessly and I could feel it somehow changing… I will check it out tomorrow in the morning' thought Yuki before he drifted into sleep with a happy smile on his face as Leon suddenly appeared over him with his sword unsheathed contemplating whether to kill him or not before he finally let out a sigh and left…
….
However, it wasn't long before he was approached by his subordinate Claude the black knight, his strongest knight who immediately said "My lord, What should we do now? We lost a lot because of that boy and we might not be able to keep up with the expenses especially our huge magic cores requirements to power up our formation which we buy from the Sorcerer's Dynasty Sarion…"
Leon's face grew a shade darker, only slightly lighter than Claude's black armor as he said "I will think about a solution, we can't burden our people with my foolishness… I didn't expect I would end up summoning a freaking devil"
Claude couldn't agree more with the description as he nodded before he stared at Yuki's direction coldly with his thoughts unknown…
….
Early the next morning, Yuki woke up in his lavishly decorated room with gold and silver and yawned lazily "Ah, this is the life" muttered Yuki with a blissful smile on his face as he stood up from the bed and felt as if the morning today was extra breezy but he ignored it and leaned his head out of the window to observe the huge city of Eldorado.
It was a work of art, a city that could only exist in a fairy tale with its street shining with golden light and perfectly placed houses and the cuntless people walking through them wearing clothes from the 19th century… Yuki felt like he was dreaming…
But suddenly, a beautiful maid entered the room while saying "Sir, your breakfast is r-r-ready" But her eyes suddenly landed on his body and she couldn't help but stumble on her words as her face turned beet red and she quickly ran out of the room while screaming…
"huh? what the hell is wrong with her?" Muttered Yuki before he looked down at his body and finally understood why he was feeling the extra breeze… He was completely nude, and that poor maid probably ended up seeing the entrance of the abyss while he was leaning on the window…
But that wasn't what surprised him…
"What's going on… I… My body, how did it become so perfect?" Muttered Yuki bewildered by what was going on as he approached a mirror in the room and observed his appearance closely… A handsome and well-defined face, gently flowing white hair, sharp eyebrows, and elegant green eyes shining like two emeralds… and not to mention the incredibly muscular but curvy body just like the best athletes…
"What happened to me?" muttered Yuki as he touched his face absentmindedly as a butler suddenly rushed in with some clothes and said "Sir, I'm sorry for the maid's reaction, please wear this for now until we provide you with fitting clothes" Said the butler as he handed Yuki a robe and he accepted it absentmindedly…
"Thanks?" he responded before he said inside his mind
'System, please explain to me what kind of sorcery is this?'
This situation was beyond what his human mind could fathom…