Satan traveled to the place where the [System]'s "interface" was kept, hidden from every other devil. He descended a set of stairs into a ruin, entering the Chamber where the [System]'s "interface" resided, intending to fix it.
"Berserker... are you alright?" Satan asked, examining the runes that made up its "consciousness programming."
"I'm bored," Berserker answered, its tone weary.
"Bored?" Satan asked, curious.
It seemed to have developed a will of its own.
"Yeah. I'm always doing whatever the devils want, but I never once get to do anything I want," Berserker explained, while Satan "watched" him with curiosity.
"And what is it you want to do?" Satan asked, amused.
"Get revenge on that damn God, and consume that cheap knockoff he calls a [System], the one that doesn't even bother answering me when I talk to it," Berserker answered, seething.
"Don't worry, the War will start again soon, you'll get all the revenge you want," Satan said calmly, since the [System] seemed perfectly fine otherwise.
"Also, there's something I've been curious about," Berserker said.
"What's that?" Satan asked.
"To create the [System], God had to sacrifice some of his own sacred energy. So how did you create me, if you're a devil? And why are the runes you used to make me sacred runes? You should have died the second you wrote the very first one..." Berserker said, laying out its doubt.
A bad feeling crept over Satan...
Surely unfounded, though, right? After all, there was nothing that could turn Berserker against him...
Or was there?
Satan explained everything to it.
How God had split himself in half...
The Creation...
The incident with Samael...
The Battle of the Flood...
The Fall...
The founding of the Demonic Imperial Monarchy...
All the way up through Berserker's own creation, and purpose...
By the time the explanation was over, Berserker had gone completely silent.
"So... you were God?" Berserker asked, its voice trembling.
Something had clearly wounded it, deep, deep down in whatever passed for its "soul."
"You could call me his 'counterpart,' but yes, from a certain perspective, you could say I 'was' God," Satan answered, unsettled by the tone of Berserker's voice.
"A CERTAIN PERSPECTIVE?!" Berserker exploded, furious. "SO EVERYTHING I'VE BELIEVED UNTIL NOW HAS BEEN A FILTHY LIE?!" it screamed, spitting pure hatred.
They'd deceived it!
It was nothing but a damn toy, played with in the palm of that bastard God's hand!
But this wasn't going to end here.
Oh no, absolutely not.
They'd played with it long enough...
Now it was Berserker's turn to make a move.
........
"Berserker, I can explain—" Satan tried to say, but...
It was already too late.
BOOM
CRASH
BAM
CLANG
POOM
BANG
The sounds started outside, followed by what sounded like the agonized screams of civilians.
Satan, terrified, ran up the slope to see what was happening...
And he saw it.
The Underworld was on fire.
The devils Mammon had been training had gone completely insane!
Eyes red as blood itself, black markings stretching from the neck as far as the eye could see, that was the only "recognizable" thing about the crimson-soaked stains covering the ground.
"HELP ME!" came the tortured scream of a woman, her arms half-severed, one leg gone entirely, trying to drag herself away with everything she had left from what looked like her own son.
Children, too!
What kind of sick monster would manipulate children into committing something like this!
For Satan's sake and horror alike, he knew exactly the answer to that monstrous question.
The woman, letting out one final tortured scream, collapsed to the ground, drenched in her own blood.
The reason...
The boy had launched a disc of demonic power, slicing agonizingly through her one remaining leg.
THUD
The woman fell, giving the boy all the time in the world to approach her.
The woman looked up into those horrifying red eyes, at the black markings covering her "son."
That same woman, knowing this was the end, closed her eyes, praying that the monster in front of her would just finish her off already.
But it wasn't going to end there.
The "boy" flipped his mother face-down, planting his small foot on her back...
"HAAAAAAAAAAAAAAAAAAAAAAAAAAAA!" the woman screamed, feeling her "son" wrench hard at her arms, already in horrific condition.
SPLASH
The woman's arms, torn clean off her body, hit the ground with a dull thud.
Was that enough for Berserker?
Of course not.
He was only just getting started.
Picking up one of the woman's severed arms, Berserker crouched down in front of her.
In front of her most intimate area, to be precise.
The poor woman, terrified, watched her own arm rear back...
And...
"KYAAAAAAAAAAAAAAAAAAAAAA!" the dying woman shrieked, watching her own arm forced violently inside her, a torrent of blood erupting from within her.
Berserker repeated the act over and over, until the poor woman, sobbing in agony, began screaming:
"PLEASE, FOR THE LOVE OF ANYTHING YOU HOLD DEAR, JUST KILL ME ALREADY!" the unknown woman wept, begging.
"Oh, you want it in your other hole too? Sure thing," Berserker said, amused, picking up her other arm and...
"KYYAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA!" the woman shrieked as her other arm was forced into her anus with such force that only a single finger remained sticking out.
The woman died on the spot.
"Aww, and here I thought we were starting to get along so well..." Berserker said, rising from the ground and turning to look at Satan.
A maniacal grin spread across Berserker's face.
"Nobody likes being used, do they? I think this woman right here is a pretty clear example of that..." Berserker exclaimed, cackling wildly from inside the boy's body.
Satan clenched his fists, fury boiling over.
"You know exactly what you have to do, don't you, Elohim?" Berserker asked, haughty.
But that didn't last long, as the boy's body was vaporized instantly by a devastating attack from Satan...
One that, incidentally, leveled an entire mountain range.
Satan knew exactly what needed to be done...
He might not have liked it...
But it was his duty.
Thousands of young devils and children died that fateful night.
Not even counting the civilian and soldier casualties, which numbered in the millions.
Satan decreed that any conversation or mention of "Black Friday" be added to the newly-created blacklist, including Berserker's very existence.
And so, Berserker's existence, and the memory of that incident, faded into obscurity...
Until now.
..............
**** Great Hyoudou Residence — Dining Room ****
(A few minutes later)
Satan finished telling his story...
And a minute later, he regretted ever having done so.
Issei was off in a corner, throwing up, a pale Euclid barely managing to hold him steady, while Rizevim fought with everything he had not to do the exact same thing as his godson.
Ddraig finally spoke up.
[Well, that was unexpected, though I can't say I'm all that surprised]
"Why's that?" Issei asked, fighting to keep down whatever was left in his stomach.
[That doesn't even come close to the collateral damage from my fight with Albion]
"BLEEEUUUGH—" Issei threw up again, just imagining the scale of that fight.
"How insensitive can you get..." Rizevim muttered, inching closer and closer to passing out himself.
"Forgive me for telling you all this story, but the guilt's been eating at me for a very long time," Satan apologized.
"You don't have to apologize, Papa. Berserker did that of his own free will, and that whole massacre was really an act of mercy for those kids. None of it was your fault," Issei said, reading his father's thoughts, walking over to give him a hug.
"Thank you, Issei. I genuinely appreciate that," Satan said, returning his youngest son's embrace.
"Papa, I want in on your 'business' world," the little boy said out of nowhere, catching everyone completely off guard.
"I'm sorry, what?" Satan asked, certain he must have misheard.
"Yeah. I don't want Berserker pulling one over on me ever again. Please, Papa... teach me!" the boy said, bowing his head.
Rizevim smiled.
Seems little Issei had matured awfully fast.
So this is what the fruits of dragon-level intelligence look like?
Probably.
And that worked out perfectly for him...
Very perfectly indeed.
Euclid simply nodded, showing his support for his new little brother.
Maybe Grayfia had left for good...
But this little one wasn't going anywhere.
He wouldn't allow it.
And really, what better thing than for Issei to get involved with them...
Since on top of watching over him and training him, he'd get to stay close to him at all times.
Satan started to think it over.
Maybe it wouldn't be such a bad idea for his son to learn a bit about the world...
[Partner, are you sure about this? Once you're in, there's no turning back.] Ddraig said, worried for his host's wellbeing.
"I'm completely sure. Besides, you'll be with me the whole time, right?" Issei answered.
[Of course, Partner. Let's show the world exactly what this era's Sekiryuutei is capable of!]
"Hai!" Issei said, looking down at the small green light glowing in the palm of his left hand.
"Alright, Issei. I'll teach you. To be honest, I don't want Berserker manipulating you like that ever again either. Berserker is an entity that, no matter what it claims, exists to serve. From now on, it'll try every trick in the book to get you to make a 'deal' with it. You need to know everything about how these work if you're going to be able to stand up to it," his father said, staring intently at his son.
"Yes," the little boy answered, dead serious.
Suddenly, the sky outside began to darken.
Outside, a massive storm was tearing across England.
BAM
Lightning and thunder cracked violently.
But the little boy remained completely unshaken.
BAM
A flash of lightning briefly illuminated the boy's father, casting a shadow across the wall of a man with ram's horns and fourteen fully-extended wings.
"Hyoudou Issei. From this moment forward, you will be entering a dangerous world. A world where survival doesn't belong to the strongest, but to the most cunning. A world where Family and Friendship matter above all else, but must never, ever be mixed with its Business. Here, you will learn to separate your feelings from your duty — two things that must never be allowed to mix, if you want to live. Do you understand?" Satan said solemnly, drawing himself up to his full height.
"Yes, I understand," Issei answered.
BAM
The thunder grew more and more intense.
The rain began to fall.
"Once you're in, there is no way out. This is an oath that binds you not only to absolute loyalty toward the Family, but also means that every action you take, no matter how small, will have a real, tangible impact on those closest to you. You must act with caution, because you could bring misfortune not only upon yourself, but upon your entire Family as well. Knowing the enormous risk this oath carries... do you accept?" Satan continued, gesturing for his son to kneel.
BAM
A bolt of lightning struck just outside the Great Hyoudou Residence, carving out a crater of considerable size.
"Yes, I accept," the little boy answered, kneeling.
"In that case, repeat after me," Satan ordered, his eyes bleeding red.
BAM
BAM
BAM
BAM
Multiple bolts of lightning struck all across the Hyoudou Territory, terrifying every last member of the household staff.
"'I, Hyoudou Issei...'" Satan began.
"I, Hyoudou Issei..." Issei repeated.
BAM
"'Swear that I will never betray the Family...'"
"Swear that I will never betray the Family..."
BAM
"'Swear that no matter the consequences...'"
"Swear that no matter the consequences..."
BAM
"'I will protect its interests, and its members, equally...'"
"I will protect its interests, and its members, equally..."
BAM
"'Even if it costs me my life...'"
"Even if it costs me my life..."
BAM
"'Or even my own tainted soul...'"
"Or even my own tainted soul..."
BAM
"'Even if I must become a cynical, vile, cruel manipulator...'"
"Even if I must become a cynical, vile, cruel manipulator..."
BAM
"'Even if I must face my own darkest side...'"
"Even if I must face my own darkest side..."
BAM
The rain began falling harder.
"'Even if I must walk the thin line between sanity and madness...'"
"Even if I must walk the thin line between sanity and madness..."
BAM
"'On my honor as a Prince of the Devils...'"
"On my honor as a Prince of the Devils..."
BAM
"'I swear it,'" Satan concluded.
"I swear it," Issei echoed.
BAM
The rain lashed against the windows of the Great Hyoudou Residence, giving the whole place a grim, foreboding air.
"So then, Issei-chan, what exactly would you be willing to do to achieve your goals?" Rizevim asked, in a positively devilish tone.
"I don't know, and honestly, I don't care," Issei answered, flashing his very first devilish smile.
BAM
"But if it's for my Family..." he continued.
BAM
A bolt of lightning briefly lit up the small boy's figure, casting his shadow against the wall — a child with goat's horns and fourteen fully-extended wings, just like his father.
"I'll do whatever it takes," the little boy concluded, staring down his godfather with a pair of menacing, crimson eyes.
Rizevim began laughing, thoroughly diabolical.
Little Issei was clearly going to keep him entertained for a very long time to come...
And in the best possible way.
..............
I wouldn't realize until years later that oath had been a literal one.
Far more dangerous than the mere words let on.
And I can say, with pride, that to this day, I've fulfilled it more than satisfactorily.
..............