In the town of Yoen, five years have passed.

Cain was now 18 years old; he'd grown taller and had become smarter.

Even so, Cain lost much of his memory of the event five years ago. Perhaps it was a coping mechanism from the trauma, but he had no recollection of what happened. The memory was forgotten and locked away.

But that terrible event still had an effect, whether it be the attack or the serum, Cain never cracked a smile, he no longer seemed innocent. He brushed off John's jokes and kept to himself, often disappearing for hours alone. His eyes grew stormy, and his voice low. 

When Cain awoke from the operation 5 years ago, John took him in. Over time Cain got used to living with him but from time to time would ask about Feick's whereabouts.

John, of course, told him Feick left town with a convincing reason and explanation.

But Cain had a gut feeling; his mind long stopped believing what it was told, not even for a second. John's honeyed words caused him to grow suspicious.

Once he got settled as John's apprentice with fake documents and the like, he would investigate from time to time.

It didn't take long to gather enough evidence to find John's claims false, which led him to the conclusion that John killed Feick. But, he could care less, Feick could also not be trusted. He did help Cain but after learning more about contaminants he doubted the old man's reasons for helping him.

He didn't know why John killed him, but over the last five years, he was treated well so it was a price to pay.

The thing that made him uncomfortable the most was the way John treated him. He would treat Cain more as an object than a person, never hiding his obsession. Yet these weren't the focal points of Cain's life. No, it was what John's serum did to him, as it changed him more than he could ever know.

After the operation, when he woke up. John found Cain's strength equal to a grown man, as a child!

His body's overall fitness was at its peak and even broke through a few physical boundaries. Of course, this is normal for those who augment themselves with viruses and pathogens.

Yet John found Cain's pathogen-reinforced body to be subpar. His body was no "Divine Body" for augmenters; it was even of a lower grade. Of course, John's research was not that shallow.

If you were to imagine a normal augmented body as a hard concrete block, Cain's was a hollow concrete block.

This hollow brick was incomplete, to finish it, one needed to fill it. This would be by adding specific diseases and viruses, adding them to the foundation, filling the hole, and therefore becoming stronger.

This development wasn't bad, it meant Cain's physique wasn't done growing, something that went against the current norm.

With was a great boon, but it also had its limitations, once Cain adds something to the formula, it's not like he can take it back out.

Nonetheless, this discovery made John happy to an extreme; if improved right, Cain could become unfathomable in physical strength; none would be his opponent!

To achieve such an outcome would require research, which John couldn't focus on alone, being stuck in Yoen and all. Many premium materials for such a project, even in all of Netherane, would be extremely rare to find. So if Cain wanted to have such a body, he would have to spend years finding and researching different things to integrate different powerful pathogens into his body.

This was still a positive! Cain now has the chance to become one of the strongest people alive.

Through the five years staying here, Cain has also studied under John and became a successful plague doctor; he's not on John's level, but he's far better than others his age.

From John, Cain learned that there is a ranking system for plague doctors from 1-5. Below grade 1 are apprentices, and it took a decade to become grade 1 without talent in the field.

John was at the barrier between grades 3 and 4, while Cain recently became rank 2, revealing he had a rare talent for diseases. 

How the grades were explained are as follows:

Apprentice: Studying to understand diseases.

Grade 1: Understanding common diseases. Those of this Grade can control symptoms and mutate them for research, but this requires a closed environment. Useless in combat.

Grade 2: Has a full understanding of most common known diseases and can control these diseases with ease, even curing people with a flick of the hand. They can also infect others with diseases they are specialized in. Effective in combat to a degree.

Grade 3: Those in this Grade begin to understand more rare and exotic pathogens as well as have a full understanding of all known common diseases give or take.

They can control the bacteria around them to infect others due to having diseases act as an extension of their will. This is done by having bacteria form together, and it requires fine-tuning and control. Extremely effective in combat.

Grade 4: This is where a Plague Doctor has a full understanding of a handful of rare and exotic diseases and starts to master a certain branch of virus.

They can control bacteria and even some viruses around them as if it were magic. The pathogens they control can be used for a plethora of things. They can infinitely increase their power as long as they increase and expand their understanding of viruses. It's not wise to fight them.

Grade 5: This is the stuff of Legend, as there always is. It is said that those at this rank can control pathogens smaller than bacteria. No one even knows how to get to this grade.

There were Augmenters, those who have undergone body modification. They cannot improve or advance in ranks. The serum they first take is the serum they're stuck with for life. All Serums have their own Ranks, similar to Plague Doctor Grades.

This was why Cain achieved something never done in augmenter history before, Cain could consider himself fortunate that he could continue to advance his augmented body.

However, John has noted augmenters are a branch of Plague Doctors. 

The case is that augmenting helps strengthen the body and shouldn't be a focus. It's an additive to the strength gained through knowledge.

To advance as a plague doctor, one has to "understand" a disease. This is done through studying them and researching them to a point where you explain everything about the disease over dinner, its target, how it travels and infects, the time it takes to infect, what it is made up of, etc.

It's like an obsession. This is also why John views Cain as an object. He is his research, his understanding.

For Plague Doctors reaching the lower Grades is easy as there are libraries that have centuries of information one can read from even if they don't have talent.

When one understands a pathogen, one can gain a sort of connection to it, which allows magical control over it. When you understand the rules the bacteria follow, you can control its path. 

John even showed Cain what a Plague Doctor's power looked like.

During one of their experiments, he gestured to a patch of mold growing in a petri dish. Cain watched as the fuzzy green mold began to move, forming a miniature tower at John's command.

When Cain later tried to simulate what John did, he found it difficult. Even if he had a good understanding of the bacteria, it was like controlling another limb. A limb that was dead.

In a sense, he was trying to use his understanding to force the bacteria to act out his will, manipulating it.

But one person's understanding can trump another, this was why Plague Doctors find or even cultivate their own diseases to be the ones with power.

To be more accurate, understanding is like a skill. This is why the diseases someone studies are important for later development.

But for one to advance from Grade 2 to 3 requires an understanding of exotic and rare diseases. At this point, no amount of common knowledge can help. Such diseases are kept to the plague doctor who studies them.

To pass on this knowledge such powerful masters take in a student to teach. In a sense, it is like handing down secret techniques.

This practice a tradition but it allows the knowledge to always be updated. If anyone ever needs to be cured of these rare diseases, the Plague Doctor can make a trip or just make the cure and send it over.

The system makes sure people have power while keeping the populous safe from disease.

But this was not all Cain was told.

"Remember, even if this way is good, it still has its drawbacks. New diseases can start to pop up without anyone to study them. Which is why I don't want you studying my diseases."

Learning about new diseases was an issue. It was way harder starting from the beginning, it got to the point where people began to search old structures and ruins to find decades-old notes for some half-extinct bacteria related to a current one.

New diseases would emerge while old ones mutate, making prior knowledge obsolete.

To be a Plague Doctor was to fight against Nature itself.

Under the current plague doctor system, even with so much knowledge, people's health will deteriorate over time until even minor illnesses become lethal.

There are examples of this. 500 years ago there was an outbreak of a pathogen that turned people into what is called a zombie but since it was a bacteria it wasn't too dangerous in the beginning. 

It spread all over Netherane and caused humanity to almost collapse. But a cure was made, saving the remaining population and allowing humans to push the bacteria to near extinction.

But even now, this disease, Zimostafacus, also known as Zimo disease, has become prevalent again. Yet none of that is important. What's important is not a thing, but a person.

Cain was a genius at studying pathogens, this might've been caused by the serum. It was a full body augmentation and infected even the brain, it was possible it could've enhanced Cain's mind in some way. 

In the case of John's serum, it was virus-based, which was rare. John was hoping to break through to Grade 4 by completing the serum and understanding the virus he was using for it.

Alas, he didn't, but he now had a new hope, Cain.

This student of his was as talented beyond belief, having long improved himself and become quite a good doctor; his favorite diseases, which are the ones he is focusing on, are Trachoma which causes blindness, and Osteomyelitis which weakens and damages the bones.

The bacteria are in the ranges of common but Cain wanted them for their effects. He hoped to use them in combat.

Plague Doctors didn't just use pathogens to attack. Some diseases were used to heal, defend, or even control others.

...

Cain grinned as he gazed out at the decaying town. After five years in this cesspool, he had adapted. The once small boy had become ambitious and had long since read every book in the local library, as well as John's private collection.

In light of his students' rapid progress, John decided to return to a Free City to acquire better resources and to find bacteria or even viruses that fit Cain and his physique.

Doing this would also allow John to study Cain more. Right now he doesn't even have a tenth of an understanding. Augmenting serums was all about reversing the effect of pathogens. To turn an attack into defense and the body into a fortress that could do both.

John even suspected the virus in the serum evolved into a strain of the Marburg virus; he's even tested Cain multiple times, and Cain's skin and organs seem to be the most reinforced and protected part of his body.

After packing all day with John for their trip to Free City, Cain looked behind them as they left.

Memories began to flood his mind. He had spent most of the last five years here alone - studying in the clinic, running errands, researching at the library.

Now, leaving, a smirk erupted across his face as he turned back and sat in his seat.

'Hah....I hope life will become interesting from here on out. I've been cooped up in a lab all my life so far.'

Cain was excited about what the future would bring.