Demons were outright evil, no relativity, prejudice, or misunderstanding there.

According to Luke's memories, no one in the tower knew how it worked, but demons were strengthened by the atrocities they committed rather than training their mana stats. The more their victims suffered, the more power they received, and new victims gave more power than torturing the same target over and over again.

Not causing a certain amount of pain for a few weeks made them suffer terrible pain themselves, so they had to decide between making others suffer or suffering themselves. Torturing willing targets didn't work either, so finding masochists wasn't a solution. Moreover, if enough time passed without getting sustenance from other beings' agony, from months to years depending on the demon's strength, they simply died. Considering only people who repeatedly made others suffer would turn into demons to begin with, it was impossible for them to sacrifice themselves for someone else.

In the tower, they were killed on sight, no questions asked.

Demons weren't a race, but rather corrupted beings that kept their original form, though some chose to abandon it for extra power. Weak or cunning demons could blend well in a magic-less and free society like Earth's, easily infecting others with Demonic Seeds.

Luckily, there were four ways of determining for sure if anyone was a demon even if they were wearing human skin.

The first was a spell that required a lot of mana of a certain purity, something Luke couldn't do yet.

The second was a magic item that Luke also couldn't craft yet, but he knew how to, and was actually easier to make than the spell. He would be able to do it a little after healing his grandad.

The third, most common way, was simply having the system identify the demons for you. Even though he now knew that the tower's system had been under demonic influence, it had still officially wanted them dead. There was a caveat though: you could only identify demons from a different species than your own.

Many theories existed about why that was so. The most prominent one was that the tower wanted the races to fight the demon menace together, and indeed, every place would have someone of a different race to identify newcomers and make rounds. However, those people could still lie, which led to issues now and them.

Now that Luke knew the Sentinel System had been invaded to a point, that race thing obviously had not been done for a good reason.

The demons had done that to create a loophole to abuse.

Either way, Luke had inspected his phoenix heart, checked his status, checked his stats... but he hadn't tried identifying other people yet. If that worked, he would have a great tool against demon infiltration as long as the system showed demons of one's own race too.

The fourth way to identify a demon was by witnessing them either using demon fire or putting a Demonic Seed in someone.

Jackson's eyes had turned red on two occasions, back when he had been breaking Luke's bones, and when he had tried to kill Luke. That, however, was just a sign that someone was using a skill related to fire, though Luke hadn't detected any skill the first time. All demons had high fire affinity, but fire was such a common element that using it meant nothing.

Demonic Seeds, on the other hand, were unique to demons. They were brain parasites that whispered and influenced the host to commit atrocities. When the host acted on it, the seed absorbed the power created by their target's suffering to strengthen both itself and the host. Such absorption was what made the seeds really dangerous, as it made even normal people or animals capable of becoming dangerous mana users intent on causing harm.

Only other mana users—or system users, Luke supposed—could protect themselves from the demons, as proven by Jackson keeping everyone unconscious while Luke screamed. If Jackson wanted, he could've killed everyone in the hospital.

Maybe he had killed some bodyguards. Luke would have to ask.

If a Demonic Seed's host was a somewhat nice person, the corruption would be slow. The constant whispering and influence would destabilize the person's psyche first. As they got confused and angry, they would do minor acts of aggression, a small push here, a foot to have someone trip there, all against people they believed deserved it. The suffering caused by such acts, no matter how minor, would strengthen both host and parasite, and give the host great pleasure. An addicting pleasure greater than any drug could provide. From there, it snowballed into bigger acts until the person submitted completely.

People who were already psychos, like Jackson, took the highway straight to power. They accepted the promise of power and already enjoyed the process required to get it anyway. They got strong quickly, and their humanity disappeared even quicker.

There was a threshold, a point of no return, after which a being was considered a fully fledged demon rather than a corrupted being. Before the threshold was crossed, they could be saved by removing the seed. However, once it was crossed, the parasite merged with the being's body completely, literally changing their brain for good. No known magic could revert that process, though many had tried in the tower's history.

If a being wasn't originally a mana user, the seed would create mana channels in them just as it merged with the brain. That's how Jackson had become a mana user himself, capable of putting everyone to sleep.

More importantly, only after becoming true demons could they produce Demonic Seeds, like the bully had done.

Jackson was already a demon, no way around it.

Fortunately, Demonic Seed production was limited by how powerful a demon was. The seed Luke had resisted was certainly the very first Jackson had created, and would be the only one he could produce in at least a few months. That's why the boy had gotten so furious when it had gotten destroyed.

Speaking of which, Jackson's words before trying to infect Luke hadn't been a lie: Luke could become a demon strong enough to kill Jackson by accepting the Demonic Seed. Demons weren't prevented from hurting each other by nature or internal rules.

However, growing stronger than the one who put the seed on you was very, very hard. A part of Luke's strength would always have been siphoned into the seed creator, Jackson. To make matters worse, it was a pyramid scheme that kept feeding the one at the top for three "generations." Old demons with thousands or even millions of seeds around giving them power were ridiculously strong.

Fortunately, the opposite was also true, young demons were relatively weak in the tower.

Unfortunately, even a weak demon was a supervillain on Earth.

Jackson was still a fresh demon. Luke hadn't concluded that just because of how weak his fire had been, but also because he had ignored the damage he would causing to his family's influence in the school's rooftop. A strong backing would make him safer and more powerful in the long term, but it took some time for demons to get used to the addicting pleasure of causing pain, and just like any addict, they became reckless if it meant getting a fix. Reckless behavior was even considered a sign of someone getting seeded in the tower, and was investigated at once.

Seeds weren't the only way to become a demon though; natural demons also existed.

Luke didn't know how to become a demon naturally, but he suspected it required a lot of knowledge about mana manipulation, and probably some strong magic power too. His memories said all natural demons to have been found in the tower had been uber strong, which shouldn't be a coincidence.

The issue was that Jackson was unlikely to be a natural demon. He had never shown either magic power nor knowledge on the arcane before, which would let him do much more than rule over a school's students. He had most likely been infected by a Demonic Seed, which meant there was another demon close enough to infect Jackson.

And him being infected led to a terrible conclusion: the Demonic Horde was already on Earth.

At least one demon had to be there to have seeded the first human. When demons were invading a new town or kingdom, they always sent a demonic monster that could reproduce fast, so there was one of those around. The only silver lining was that the monster had to be a magically weak one, or they wouldn't function on Earth's low mana environment.

Still, the issue remained: somewhere on Earth, monsters were already increasing in numbers and preparing to conquer the whole world, and humankind was completely in the dark about it.

The system would take six months to become fully active, and Luke had taken it as a distant and abstract danger to worry about later. He couldn't have been more wrong. Demons were already here, and the system was too late to give humankind the power to fight back.

It even explained why the system was pushing mana into Earth even though it would also strength the demons and let stronger monsters invade. The only way for any race to fight demons was with mana or the enhancements given by the system. Even if Luke taught everyone about mana channels, not everyone would be interested in magic or even have talent for it. The system could give them a workaround in the form of physical stats.

Lucky for Luke, he was interested and at least a little talented, since he was managing to build his mana channels.

Yet, it was still too slow.

If Jackson had attacked Luke's head, the latter would be dead, phoenix heart or not. The only reason Jackson hadn't, if Luke had to guess, was that he didn't trust his weak demon fire enough to burn through bones, and Luke's brain was protected by his skull. As for why Jackson hadn't gone for Luke's throat, that was probably because the cervical collar had been covering it, and sheer luck had made the demon consider it protected. After all, he hadn't been thinking straight because of the need for another fix.

At least the rage Luke had shown had made the demon see him as good seed potential. Demons usually infected emotionally unstable people or psychopaths first, as they were easier to corrupt. That might even have made Jackson decide to infect Luke rather than Sakura.

But what if Jackson had seeded Sakura instead? What if his bodily heat hadn't tripped the fire sprinklers? What if Luke hadn't had the phoenix heart, had been seeded, and had hurt the girl he liked and who had just declared herself to him, just so he could grow strong on her suffering?

Despite all the knowledge in his brain, despite how much potential he had, Sakura had survived unharmed out of luck, and that made him feel terrible.

He decided right there: not again.

Never again.

He was afraid. He was terrified. He wanted nothing more than hide and let other people deal with the demons.

But he was a warrior, wasn't he?

It was in his blood, right?

He decided right then, right there, once and for all, that his days of bowing and scraping were over. He would grow powerful, and use that power against his enemies, no matter who they were.

Even if he peed himself in a fight to protect those he cared about, even if his whole body trembled as he faced foes he knew could be much stronger than Jackson, even if his brain screamed at him to run away, he would go forth.

He would fight for the people he loved.

To the death.

Fighting for the ones he loved started with preparing himself for battle. Luke focused into his soul, controlled some mana into becoming a chisel and started carving runes into his mana core.

Engraving the runes was the most dangerous and painful part of building a mana channel. He would hurt his soul by chiseling bits of it away to do it.

Both body and soul were needed for living beings to keep alive. Unlike the body though, the soul didn't have critical spots that would cause death if damaged. You could kill someone by crushing their brain or taking their head off, but doing something similar to the soul wouldn't kill them. The only way to kill the soul was destroying enough of it, and the amount was different for each person. Some would die as soon as a quarter of it was removed, while others would survive even with only a quarter of their souls remaining. There was no rule to it or explanation to it, though some theories suggested it had to do with the will to keep living.

Luke focused and chiseled.

Pain similar to needles piercing through every cell of his body coursed through him.

He chiseled.

He felt like he was being skinned alive and his bare flesh was being sliced by a thousand knives.

He chiseled.

It was like his bones were burning and he couldn't get them away from his melting body to cool them down.

The pain was terrible, and he was only taking small bits of his soul each time. The bigger the part being taken away, the more it hurt. After at least five percent of the soul was taken away, lingering pain would stay with the person, and the larger the part missing, the worse the pain was. That was the main reason that building mana channels didn't involve removing any part of the soul, but just pushing it away with a drill.

Mana runes, however, had to be precise, and it would take way too long to create the perfect edges required just by pushing the soul away. Weeks at the very least, months at worst. It was just way more efficient to withstand the torturous pain.

The soul healed anyway. It was slow, but in at most a year, the tiny bits he had chiseled away would recover. They wouldn't regrow in any part where mana was going through, but the lost mass would return to the soul.

So Luke kept going.

The pain was greater than anything he had ever felt except the fight between demon and phoenix in his brain, but every time he thought of stopping, he thought of Jackson's threats toward Sakura. He remembered the demon's face so close to her. He pictured his dirty fingers caressing her face.

Sheer anger pushed him forward.

His phoenix heart burned fiercely all the while.