"Argh!" No matter how resilient he may be, the boy still has a breaking point. The consumption of the strange potion brought him pain he had never experienced before. 

If one would look at his insides, one would see the potion breaking down and becoming a red mist that is seemingly alive and is trying to bury its way out but it surprisingly couldn't. This is one of the effects of his 'advancement' or 'Metamorphosis'. As such, the energy just continued to wreak havoc inside.

Anguished howls and cries filled the room and into the corridors. The boy is now clutching his stomach while fidgeting on the ground, saliva drooling from his mouth.

Such a sight gives the old man delight but now is not the time for that. He commanded the boy to exercise the breathing technique while also helping him sit back in a meditative posture.

With the help of the breathing technique, the energy in disarray became somewhat tame as the soothing 'refined energy' commonly known as [Nether] that flowed from the boy's heart carefully enveloped it. It slowly guided the incorporeal crimson mist back to his heart through the circulation channels his advancement 'carved'.

After the red energy completely fused with the heart, the boy's heart rate relatively slowed down.

Thump

Thump

Thump

...

Dozens of seconds later, a change happened.

THUMP

That powerful beat comes with a wave of intangible energy that covered the boy's body inside out.

After that, the second heartbeat occurred.

THUMP

Small veins protruded from the left and right side of the membrane covering his heart causing another tormenting pain to wash over the boy's sanity.

It swayed left and right. It appeared to be alive as it squirmed and formed complex branches.

THUMP

The veins grew in length in every beat but they also send waves of pain throughout the pitiful boy's body and psyche. He was already feeling fatigued and dizzy because of the suddenly reduced heart rate and when combined, his state of mind is crumbling.

But his desire to live and achieve freedom kept him going. His very nature. Every breath feels heavy but he endured it with gritted teeth. 

By his side, the old man is carefully examining his condition while mumbling to himself.

Him not exploding into a bloody mess is a good sign and upon seeing this, the old man was ecstatic. It means that his body could endure the process and that there is a chance for full [Integration]. But a chance is still a chance. It now depends on whether the little imp could endure it to the end or whether the potion is enough to fully carve the [Monster path]. 

If not, the old man would have to wait for another supply of [Thousand Arms Monkey King]'s heart which would take a very long time. 

Generally, it takes 3 - 5 potions to fully integrate with a new set of monster paths but for more potent and strong monsters, 1 - 3 would be enough but it would still depend on the individual's 'talent', hence, this is a gamble for the old man.

Minutes have passed but the boy is still shivering from pain and groaning from time to time. The old man on the other hand is just watching impatiently on the side with his hands crossed on his chest. 

Unable to contain his curiosity, he used his 'bandage tentacles' to tear the boy's linen shirt off revealing a toned but immature body riddled with countless hideous scars of different shapes and sizes. 

The old man silently circled around him, trying to find something, and soon enough, 2 red spots formed both below his shoulder blades. Those 'spots' are the endpoints of the monster paths that will allow the kid to use the same ability as the Monkey king. It is generally called [Runes]. Those marks would be concealed shortly after fully integrating with the potion and would only appear when using the ability.

Mesmerized by the sight, the old man's eyes widened as he silently gasped. A smile was back on his thin lips. He restrained himself from having a hearty laugh afraid that it will distract the shivering little imp.

The process of 'drawing' those runes strictly depends on the origin of the energy which in this case, the monkey king so all the old man could do is wait before interrogating the little imp of his experience during the process.

The old man knew all too well that the only reason for the successful integration is because the boy's physical condition, talent, and tenacity are top-notch, hence, for the potion to have a higher success rate, he would need to refer to his experience to make proper adjustments.

Everything is happening extremely smoothly that the old man couldn't help but make the same hand sign he made earlier while praising the great Erebus, the revered God in this world.

Unfortunately for him, a calamity was bound to strike him from the very day he got his hands on the main ingredient of his "Masterpiece."

•••

Crimson red fur covers its body except for the chest and head area as black metal-looking 'armor' covers most of its chest, 6 limbs, and the tip of its long tail. If one would look closely at those 'armor', one would realize that it looks almost like black tinted glass, almost transparent.

Its snout is quite long much like dogs and its long 'eyebrows' fluttered in the wind.

It stood in front of an abandoned fortress, to be exact, one of the biggest buildings made of stone. Its outer appearance is like a badly destroyed tower and one wouldn't be able to guess that inside would be the laboratory used by one of the oldest alchemists in this land.

Sniff

It sniffed and a disturbance appeared in the air or to be precise, the ever-present black mist called [Netherworld Energy] or [Nethergy] for short. Now sure that the smell of its mate is inside, it viciously sprang forward building a strong momentum before ferociously smashing the steel door with its heavy fists.

BANG!

It was followed by a barrage of punches. Each of its 4 fists creates afterimages and each hit leaves dents on the reinforced steel door.

One could only imagine how thick and durable the door is. After almost a minute of attacks, the beast paused.

Ripples appeared in the air as the beast stared intently at the dented steel door. It took a few steps back before grunting calmly.

An instant later, crimson red lumps of unknown composition began to form at its back. A pair down its shoulder blades and 2 pairs just inches below and above the said spot.

It slowly formed into 6 bloody colored arms that completely resemble the Monkey's own long and muscular limbs.

Now that it's fully formed, its composition resembles the same material as the monster's 'armor' obviously except for the color.

The aura of the monster drastically changed from being a rabid beast to a Deity that descended on the mortal world.

Feeling the strength flow throughout its body, the monster stretched its joints for a bit before stomping forward just like before. Its brawny legs don't lag in strength as it's every step leaves cracks in the stone path.

With a crazy momentum, its first punch landed with an explosion, and just like before, a bombardment of strong punches rained down on the reinforced door.

With that many arms, one would expect that the monster's movements would be clumsy but if one would—or could look at the swift blows the monster is making, one would see that its movements have a perfect rhythm where none of its arms hinders one another. It also reaches a few dozens of hits per second and countless afterimages could be seen. Hence the name [Thousand Arms Monkey King].

Just a quarter of a minute later, the door or to be exact, the sturdy hinges collapsed. With a sound akin to an explosion, the heavy and completely dented steel door flew forward and crashed with a loud sound into the flight of stairs leading downwards.

In the instant that this happened, a dark-red colored sphere was flung toward the monster taking it by surprise.

•••

Fwoom!

Seeing that his attack landed, the old man's expression remained calm. This wasn't unexpected and in fact, impressive as his emotions are currently in turmoil right now. However, that is an issue for later.

The sphere that bursted from his outstretched palms is actually made out of flames. The darkish red flames of the infamous [Infernal Slug] to be exact.

The moment the sphere touched the monster, it made a soft explosion. Like a blob of mud, it 'splashed' in the monster's torso, spreading the flames.

The monster instantly felt the burning sensation as its protective armor couldn't fully block the attack. It immediately tried to extinguish it with its hands.

However, upon touching it, the flames also clung to its palms.

This opportunity wasn't wasted as the old man finished conjuring another sphere of fire.

Fwoom!

Pa!

Another attack connected. This time, the monster couldn't endure anymore and began to hurriedly back away.

The smell of burned hair permeated the air as the flames slowly burned not only the monster's skin and fur but also the energy it is using to keep the [Manifestation] of its armor.

This is the nature of this flame.

Fortunately for the beast, the damage it can actually cause isn't that serious as monsters possess a relatively great regeneration ability.

But it still greatly annoys the creature. The reason why the monster backed away wasn't just because it doesn't want to get hit anymore but to also extinguish the flames.

With wariness in its eyes, the monster began acting its intention.

This process is generally called 'shedding'. As the name suggests, it is to segregate the unwanted 'skin' or on other occasions, carapaces and shells.

What the monster did wasn't anything special. From its heart, the [Nether] bursted out forcefully supplying its armor and in turn, those black protective 'shells' began to grow.

It slowly covered the parts where flames are clinging to and in turn, those flames could only burn the monster's [Nether Armor] instead of skin and fur.

After that, the monster 'cuts' its connection with the armor, and without the supply of energy from it, the [Nether Armor] along with the flames disintegrated into nothing in the air.

This process lasted for less than 10 seconds. Quite long but the monster wasn't worried as its keen sense of smell indicates that the foe didn't move an inch in that span of time.

Or at least, hadn't yet.

At this moment, its sharp senses tingled. Without hesitation, it lunged towards the left with Its hands in a grabbing motion.

However, none was there. It carefully strode towards the corridor down the flight of stairs only to find nothing.

The monster grumbled, now sure that it did not made a mistake. It aggressively sniffed causing a disturbance to appear in the [Netherworld Energy] that is present in the atmosphere and moments later, concluded something.

The enemy is constantly moving.

It is simply because the scent that lingers in the air is currently scattered. An ominous feeling arose from the monster's heart the moment he realized this but to the creature, this was anything but serious.

The next few minutes were spent attacking places with a significantly strong scent but not one landed. This greatly frustrates the monster. 

How could a sentient being endure being played around by any creature with a lower life form than itself?

Furious, the monster began rampaging around mindlessly. It smashed everything in the vicinity and threw debris here and there in hopes of hitting the pest but unfortunately for the beast, not one did.

It now started to doubt its senses. Was I wrong all along? If the monster could speak, he'd be uttering these words vocally.

However just as the monster is having these doubts, a considerable change occurred.

•••

Seeing that the monster is finally being affected by the corruptive invisible mist he's presently releasing from his mouth, the old man revealed a sneering expression.

The old man is using the monster path ability he obtained from a [Toag]. An enormous frog-like creature located at the furthermost area of the 'Cootes Bog'—a huge swamp filled with creatures adept at using poisons and corruptions.

Its effect is mainly about releasing an invisible corruptive mist that can influence the Nethergy in the surroundings to 'corrupt' or 'poison' anyone who absorbs it to themselves.

Initial effects would be sluggishness of the physical body and the circulation of Nether in one's channels. Prolonged contact could lead to fully 'Tainting' the corrupted person transforming them into mindless beasts that would wreak havoc on anything they see or their hearts would outright explode on the spot.

The said monster is currently experiencing the initial stages of the corruptive energy. Manifesting both its 3 pairs of arms and the Nether Armor consumes Nether to keep their forms and generally, monsters have the ability to automatically absorb the Nethergy in the surroundings.

This leads to the old man's ability to easily affect the monster and it continues to do so.

The Monkey King Species attained sapience hundreds of years ago because of the Netherworld Energy that suddenly enveloped this whole planet. Through mutations caused by the strange energy and their adaptations to the new environment, they changed to be what they currently are right now.

And they are certainly not stupid.

It slowly realized and connected the dots.

The Old pest suddenly vanished into thin air but his scent still lingers. What could he possibly be doing? Why not just run away? These questions were answered in a harsh way. The discomfort that comes from the corruption finally hammered the last nail in the coffin for the beast.

These creatures always dominate anything that comes their way. It became both their strength and weakness.

Pride, confidence, and arrogance. These traits are what also convinced humanity to call them 'Kings'. They climbed up the food chain through brute force, smashing and breaking their way up with practically no effort. 

These inherent traits became their weakness in the sense that they always underestimate the unknown. They are like frogs in a well. And also because of that, they can't fully utilize their potential.

But now—the prideful King, for the first time in its long life finally realized how big the world is.

In fury, the monster finally decided to go all out.

Oob...

From its body, a dim scarlet wave of energy instantaneously gushed out. It swiftly expanded and covered over 100 meters in diameter from the monster.

Moments later, its 'manifested arms' undergone a transformation. It grew in size, now reaching 1.5 meters and sharp spikes protruded from all of its joints and strange patterns grew alongside it giving off an ancient aura.

The Netherworld Armor has also changed. It now has a tinge of red and its form morphed into resembling full body armor that Vanguards use.

The sudden influx of energy also forcefully suppressed the corruption inside the monster.

From a rabid beast to a Deity and now, the monster resembles a Bloody fiend that crawled out of hell to unleash its fury on the mortal world.