Reincarnated With The Strongest System

'Seventh Sanctum, it has been a while,' William said as he looked at the entrance of the Forbidden Ground in front of him.

He had many memories about this place, and even remembered them fondly. If not for Lilith and him falling into the River of Samsara, he might not have met his future daughter, Raizel, who had allowed him and Lilith to give their relationship a chance.

William walked straight towards the entrance with a mischievous smile on his face. Back then, the only thing he could think of was on how to survive in a domain that was surrounded by countless Myriad Beasts, who could easily end their lives as if they were just cutting grass.

Now, things were different.

'Yes,' William mused. 'Now, things are different.'

As the mists faded in front of him, William appeared in a familiar scene. It was the same forest where he had appeared in the past, and it made him feel nostalgic.

"Go, and fly over this entire domain," William ordered as several portals appeared around him.

The Rainbow Birds all flew in different directions, helping William map the entirety of the Forbidden Ground.

Back then, he was only looking for the Hall of Thunder and had no time to explore the Domain in full. Now that he was looking for an SS-Ranked Dungeon, it was time to check every nook and cranny of the Domain that he planned to conquer as his own.

In just a minute of appearing inside the Seventh Sanctum, a third of the Rainbow Birds had died after they were attacked by the Millennial and Myriad Beasts that lived inside the Domain.

William smirked as he turned into a black mist and headed towards the West, where the majority of his forces had been decimated.

Several Vultures, with a wingspan of six meters, circled the sky as they attacked the Rainbow Birds, whom they thought were all food. However, to their dismay, these Birds had a very explosive personality, and chose to self-destruct inside their mouths, causing them pain and suffering.

When William arrived at the scene, a dozen giant black vultures that went by the name, Sorrow Talons, could be seen attacking the Rainbow birds who were fighting back by cursing at their enemies before self-destructing.

"Eight peak Millennial Beasts, and four Myriad Beasts. Not bad," William muttered as he instantly appeared in front of the largest, and strongest among the Vultures.

Without even a word, William slapped the giant Vulture, sending it crashing towards the ground like a tennis ball. 

The Vultures that saw this scene, immediately flapped their mighty wings to retreat, but William had no intention of letting any of them get away.

With just a few slaps, all the Vultures crashed on the ground, shrieking in pain.

"You guys will serve as good cannon fodders," William said as he pressed his hand over the Alpha of the Flock, and forcefully corrupted it with the power of darkness.

The Myriad Beast struggled with every fiber of its being, but it was only able to last for a minute before its consciousness was completely overwritten by William's power. 

The Vultures who saw this immediately shrieked in panic, and even tried to beg William to have mercy on them, but  the Half-Elf didn't give an ear to their cries of regret.

One by one, William had made all of the Vultures his subordinates, and ordered them to fly around the Seventh Sanctum, and take over the duties of the Rainbow Birds that they had slain.

As more of the Angray Birds died, William's subordinates grew in number. The scary part about this was that the newly added monsters in his Legion were all Peak Millennial Beasts, and Myriad beasts.

An hour later, B1 and B2 found a nest of Terror Rats, which made the Half-Elf's devilish smile widen.

"Finally, I found you bastards," William said as he used his Lightning Strider Skill to arrive at the location where the two dumb birds find their quarry. 

William had specifically ordered the Rainbow Birds to alert him if they saw any giant rats in the vicinity. The Half-Elf had a beef to settle with them, so he was incredibly enthusiastic after his subordinates found their lair.

As soon as William appeared in the sky above the Terror Rat's Nest, the rats that were outside guarding the entrance of the nest all hissed at William like snakes. 

"It's not only you guys who like to get revenge on people," William stated. "I'm here to pay all of you back for the traumatic experience that you gave me and my wives back then."

William spread his arms, and a black dome of light engulfed the Terror Rat's nest, as well as the ground under it. He had no intention of letting any of the rats escape, so he trapped them inside his Darkness Domain.

Soon, hundreds of rats shrieked at the same time when William released the aura of a Demigod. 

The Terror Rats were monsters who liked to bully the weak and feared the strong. If their enemy was someone that they couldn't beat with numbers, they would use dirty tactics to get their revenge.

Unfortunately, they were up against a newly ascended Demigod who was itching to try his powers on the Myriad Beasts that bullied him back then.

A minute later, several powerful explosions shook the Dark Domain, as William unleashed a barrage of Darkness Beam at the Terror Rat's nest, making its inhabitants scream in pain and fear.

After the last rat had fallen, William once again used the method that would convert all of the rats to become his subordinates in the upcoming war. In regards to high-end monsters, the black-haired teenager was no match against Felix's forces, the Holy Order's forces, in addition to the combined armies of the Alliance. 

However, he planned on converting all the monsters inside the Forbidden Domain to make up for the lack of strong fighters in his army. Even though he didn't have any Pseudo-Gods, aside from the Black Phoenix, his personnel now had several Myriad Beasts, with the Fortaare Death Worm being the strongest of them all.

The Lord of the Desert was already a Pseudo-Demigod, and was only a step away from reaching the Demigod Rank. William was planning to give it a breakthrough, by allowing it to consume the Power of Darkness, but that would weaken him for an entire week.

This was why he hadn't done it yet because he still had many things to do.

"Scurry along, little rats," William ordered as he commanded the Corrupted Terror Rats to scatter. "Find me the dens of the strongest beasts in this Domain. Go. now!"

The Rats shrieked in obedience as they split into several parties and scoured the land, looking for the Monsters that their new Master wanted.

By the time the sun was about to set in the Central Continent, the Seventh Sanctum, that was known to be one of the most dangerous places in the World, found itself being taken over by the black-haired teeanger, whose goal was to create a monster army that would make everyone in the world cower in fear.