While the both of them were sitting under the tree in Uehara's mindscape, Volkarin continued.
"I'll explain this part first since it will be easier to understand why ki is harmful to demons. Demons are widely known as chakra-given-sentience. Chakra is a combination of all six elements. Now we come to ki. Ki is what angels wield. Ki has absolutely no trace of elements in it and so what happens when demons come into contact with such a pure energy is that it immediately upsets the elemental composition that makes up our bodies. If we come into ki on a long enough time-basis, we will cease to exist since the ki will disrupt the elemental ratio forming our bodies. It's like saltwater and freshwater. They come from the same root but have developed differently. The same applies to angels. Chakra will also harm them because their purity will be tainted by our elemental composition."
Seeing the disguised look of eagerness on the face of his son, he carried on.
"Each race has their own domain or planet. If a demon were to go to a planet full of angels, they'd immediately feel like millions of parasites were trying to crawl into their body. The same would apply for angels if they went to a planet full of demons."
After saying the last part, he sighed.
"Each race would've left each other alone, were it not for the birth of humans. The day an angel and a demon came together to conceive a human was the worst disaster that could ever happen."
Uehara was surprised when he heard the last part from his father. He knew that his father's hatred for humans was beyond them being foul-smelling to demons.
"How so, father?"
Uehara's voice came out lower than usual once he sensed the veiled anger behind his father's words. The leaves themselves seemed to shake at his anger.
"Because son, humans can drink both salty and pure water as well as bathe in both."
Uehara instantly caught the meaning.
[Humans can choose to use either chakra or ki and can also enter either domain without consequence.]
Volkarin frowned. Looking into the cloudy skies, he spoke.
"As the humans multiplied, no one paid any attention to them since they had very meagre lifespans, so they weren't a threat. It wasn't until the angels started revealing themselves to humans as their god that things started to look bad. Demons were defamed by the angels and humans were taught to treat them as lowly existences. That was irresponsible on our part. Because us demons generally don't care about external matters and only focus on ourselves, we never noticed that the angels began to secretly train the humans in the art of ki-manipulation. After millions of years, humans finally began their mission to exterminate demons and they almost succeeded. But…"
A smile appeared on Volkarin's face, completely erasing his previously angered expression.
"...failing to kill me proved to be the worst mistake of their lives. After two million years, Karina and I began exterminating every single human that we could find. After rendering humans extinct in one universe, we would go to another universe and do the same."
Uehara was wowed by his father's feats. Imagining the scene of so many planets with human inhabitants exploding awoke the desire within him to do the same. But as those thoughts surfaced, a pressing question entered his mind.
"But what about the primordials dad?"
A wide grin displayed on Volkarin's face.
"There's one thing I love about the primordials son. If you're killing humans, they won't intervene no matter how many you kill because they also recognise that humans themselves are an anomaly that should've never existed as they have the potential to pose a threat to the balance of existence."
Uehara looked down in contemplation before he asked.
"Then, why didn't the primordials exterminate the humans?"
"Simple. There are many strong demonic gods who were alive that could destroy the humans. I was simply the one who took on the job of destroying them myself."
Uehara was confused even further.
"But then why didn't they fight against the humans?"
Volkarin ruffles his son's hair when he sensed he was close to being angered.
"Because son, it is extremely hard to permanently kill a demon. You would need to use hakai or something similar like my void chi to permanently kill a demon. The reason it is so hard to kill a demon is because we will always reform no matter what. Whether it be now or a hundred millenniums later, we will reform stronger than ever before. Chakra is everywhere and you can never fully erase it, only weaken it. Regardless, demons would use that chakra to reform. That was why the demon gods didn't do anything since they saw it as a chance for the demon race to become stronger. Although the humans were fierce, none of them had hakai and the angels knew they'd have to face the demon gods if they tried any moves."
Uehara became confused when he remembered Volkarin's earlier words a few years ago.
"But father, you said surins are extinct. Does that mean they can't reform for some reason?"
Uehara immediately sensed Volkarin's change in emotion. He could feel a deep, hidden anger resounding within him.
"Yes and no. When I awoke my mandala, the souls of every murdered surin was absorbed into my eyes and I gained all sorts of knowledge. With their souls residing in my eyes, I knew I could free them at anytime to reform but then they would be vulnerable for anyone to snatch. Surin souls are very valuable and humans would love to capture them and use them as conduits to fuse with the demon spirits of other demon races or farm them."
"Demon spirits?"
Uehara was greatly intrigued.
"Demon spirits are demon souls that have regained their sentience but have not formed or do not have a physical body. Humans wait for a demon soul to turn into a demon spirit before subduing it and absorbing it. That way, they could gain the power the demon had when it was still alive."
"But why don't they just fuse with demon souls then dad?"
"Because demon souls can't evolve. It's like a cultivation. Harvesting a plant too early would yield no benefits. But waiting until it is fully mature will result in more benefits and also possibly gaining seeds to use the next time you cultivate."
His mood then turned grim.
"If they wait enough for a surin's soul to reform a physical body, they would be able to snatch the blood and drink it while killing the surin again and absorbing their soul to inherit our ability to host other demon races. I didn't want that to happen to my people so I knew I had to kill every single human in existence first before I can finally revive my people with peace of mind."
Uehara was greatly surprised by this new information. He knew surins were the perfect hosts for dragons and yokai to reside in but he never imagined humans could exploit that aspect by absorbing the souls of surins. He was going to ask what the use of the blood was for but he then remembered how Lazarin had told him how humans who ingest the blood of surins would inherit most of the traits of surins while also becoming vampiric as a consequence.
He decided to redirect his question.
"Then…what about the angels, father?"
"Initially, I wanted to revive my race before I could mount an offensive against them but they attacked me first. When I was 28 million years old, the leader of the angels, who's name was Brain, attacked me. In retaliation, I defeated him but didn't manage to kill him. But I was able to destroy his home planet with my void chi and I went a step further and destroyed his home universe, effectively wiping out eighty percent of the angel race and nearly brought them to the brink of extinction since over ten percent of the remaining angel race were devils who wanted to kill the pure angels. That was also when the primordials started hunting me. When they couldn't find me, they started helping Brain to become stronger."
Uehara restrained the budding anger within him.
"Aren't the primordials supposed to be neutral in everything, father?"
"Yes they are son. But they had no choice but to choose a side when they could no longer find me."
Uehara was confused and started to doubt the power of the primordials.
"They could no longer find you?"
A smirk appeared on Volkarin's face.
"The moment I entered the 13th Gate was the moment when they could no longer find me and they had no choice but to help Brain if they still wanted to maintain balance."