Satanael does know of the Peerage System, as well as its Heaven counterpart, but he chooses not to use, at least not now, due to how unstable it is. How can a weakling overpower a much more powerful opponent with the help of a chess piece instead of striving to become stronger himself?

A side note, no, God didn't unseal Satanael and he didn't even bother to find a way since it functions entirely different to the most common and obscure types of seal.

~Chapter 1~

There were several centuries-old records kept in every realm depicting a handsome young man in his twenties with blood-red yet not vampiric eyes, a jet black hair with small but noticeable golden trims and on his back was three pairs of both demonic and angelic wings. In his possession was an exotic but powerful sword that was reported to be capable to destroy the world and a set of armor that was so tough that the most powerful spells could not leave a dent. Various sightings of the man thorough the span of history implied that he had a hand in many historical events. It was him who averted the tragedy that would have become the tale of Brynhildr and Sigurd; it was also him who rescued and prevented the priestess Medusa from becoming the monstrosity Gorgon; the hatred of Adolf Hitler toward the Jews was also his doing. These were just some notable ones among the machinations that this mysterious young man caused.

There was a short yet absolute rule in all worlds: do not engage in combat with the Alpha Legion. No one knew of this Unit, except that they had been once the personal guards of the King of Ruin when he was alive. Their number was greatly reduced but their reputation of ruthlessness and brutally executed operations inflicted fear to everybody. Very few individuals that had met this Legion recognized the Lord of Locusts Apollyon, famed Dragonslayer Sigurd, Raven Lord Corvux Corax and even the Wolf of Darkness Cerberius among the only ten members. Famous Librarian Lorgar Aurelian of the Church, born 1578 and died 1623, wrote in his journal during the last days of his life that during the Battle of Megiddo, he witnessed the very same young man from the old scriptures in the Great Library of the Church giving orders to the dreaded Unit in the three-way fight against both the angels and their human warriors before emerging victorious with little to no casualties. Lorgar was among the POWs and got the precious conversation with the leader of Alpha Legion himself. To his horror, he was the King of Ruin.

Surprisingly, Satan just wanted a small conversation with Lorgar over the topic of belief. The Librarian was surprised at the fact that Satan was a bit disappointed at the depiction of him in the Church. Urged by his curiosity, Lorgar asked many questions about the Heaven and Underworld. Satan answered them all with his genuineness, all of which would later be written in books and distributed widely in the Mortal World. Majority of the Church declared his works heretic but the more level-headed figures found the information massively useful and combined with Lorgar's objective perspective, they were convinced and thus allowed the distribution to continue, though the knowledge about Underworld and its habitants were restricted and only the members of the Church could read them.

To the citizen of Underworld, Satan was their most beloved king, even above the current rulers. That was the reason when he and the Alpha Legion appeared during the Civil War, both sides wanted his support. Much to the Old-Satan Faction's dismay and rage, he chose the Resistance. The Alpha Legion almost singlehandedly destroyed their army. Despite his best effort, Corax could not capture all the Satans except for Katerea Leviathan.

Katerea was stripped of her robes and was imprisoned in her former chamber. The Emperor of Pandemonium personally visited her, accompanying him was Cerberius and Ludger von Weinberg, his spymaster and expert interrogator. He ordered the two to stay outside to guard while Satan himself would meet the Leviathan. Satan took off the sinister helmet to reveal his ever youthful face to the blushing Katerea. He spent the next two full days to talk and persuade her to abandon the wrong and old ideology of the Old-Satan Faction. It was difficult, especially her hatred toward the current Leviathan, a young and powerful girl from the Sitri Clan. He ordered Ludger to gather as much as possible about this Serafall Sitri.

"I see. No wonder you lost to her, Katerea." Satan said while looking at the documents. "Although you are the direct descendant of Leviathan, this Serafall girl inherits the power to manipulate ice from my general, which really bothers me if the Leviathan back then was actually a Leviathan or just a Sitri taking that name."

"My lord, I have no excuse for this failure but please allow me to fight her again! I will take my rightfully title back –"

"No Katerea, you have a much more important task right now." Satan motioned Corax to present the map of Underworld. "General Corax has confirmed the location of Creuserey, Shalba and Rivezim along with their troops. It seems that Shalba is trying to get in touch with you for obvious reasons. The Raven Lord is jamming the magic signal under my order." He looked at Katerea. "I ask you to put aside your rivalry with Serafall Sitri, as well as the Resistance, to cooperate with them to help me identify your mysterious benefactor. Can you complete the task, Katerea Leviathan?"

"…My lord, that I can accomplish but." She was unusually nervous today, Satan noted. "If I succeed, please include me in your Peerage!"

Now Satan and his present generals were at lost.

"Peerage? What is that? If you mean joining my Legion, you are already in."

"No! I mean, your personal Peerage." Katerea was fidgeting in her seat. "I want to fight alongside you just like the first Leviathan. I want to be your Queen!"

"…I can't comply your request Katerea." Satan shook his head. Katerea looked like her world was collapsing when he made a deadpanned face. "I don't even know what the heck is Peerage, how can I make you my Queen?! And I never have a Queen even back then!"

Katerea almost face-palmed but chose not to as it would be un-ladylike and disrespectful to her king.

"I-I see. If you want, I will explain this wrenched Peerage system to you."

"Not now, let's focus in the current matter first. You will rejoin the other Satans for the time being and report to me any suspicious activities, understand? Furthermore, if you are compromised, crush this pendant. It serves as an emergency warping spell that will teleport you to my location and alert any Alpha Legion companies nearby." He produced a small pendant and gave it to Katerea. The woman gracefully received it and wore it immediately.

"One last question, my lord. What are you going to from now?"

"Ah, that's a good question. I feel it's not the correct time to reveal my presence. I already instructed Apollyon to handle the politics in my stead. In the meantime, I will return to the Mortal World to keep monitoring the Church of Man and try to recruit more exceptional individuals to my Legion. Good people are hard to come by these days, you know."

-Present-

Rias Gremory and Sona Shitori eyed the new transferred student with interest and suspicion. A ward last night informed them that it detected a Fallen Angel wandering way too close to the human's populated areas and just a minute later, the signal disappeared. It also recorded a high level of energy surge which was on par if not surpassed the Ultimate class. It wouldn't have been too bad if Sona hadn't brought up the fact that even Rias' brother, Sirzechs Gremory the current Lucifer, only got to the Ultimate class in his full power and this one's reading reached the highest peak of Ultimate, a feat that only the original Maous from the Great War area were capable of, excluding Satan himself.

This man, Kagami Nakamura, just happened to arrive at Kuoh an hour prior to that event too, according to her family's agent at the airport. And their readings had already shown astonishing numbers.

"Rias, I think you should not approach him with it." Sona leveled her spectacles and stated. Rias just snorted playfully at her.

"You are just worried about me hogging him first."

"While I would never back down for a challenge like this, he seems to be out of our league." Sona said as if it was a matter of fact. "Not to mention, you already got that Hyoudou boy."

"We Devils are greedy, Sona." Rias chuckled at her rival before retreating to her club's room. The Sitri girl kept pondering over the reports of recently sightings of the Lord of Alpha Legion in Japan. Was it a pure coincidence or something was very wrong since a particular message from Kyoto said about seeing a man with characteristics identical to those of this Kagami Ichirou.

Speaking of the man, he was amused at the conversation between the Devil girls that he ignored a furious Perverted Trio addressing about his good looking and typical fantasies they would boast daily. Twirling his fingers a little, Kagami let out a psychic energy wave that sent those who being supernatural on edge. This should be enough to tell the stalking little girl behind him that he did not want her presence at all.

'So, this is the Red Dragon Emperor brother Helel spoke so highly.' Satanael mused at the flinching Issei Hyoudou, particularly at his left arm. He could see the crimson reptile cowering in fear at his power since in the past, Satan once had an interesting conversation with the Welsh Dragon that left the latter scarred in both body and pride.

'I will see it myself that you are worthy of Helel's expectation.' Kagami turned around and walked off before his grin grew. 'Because otherwise, I will definitely destroy your entire soul for making me waste all these years of waiting.'

Later that day, Kagami was contacted by Ludger. The captain informed that there were commotions in the Church. An extremely valuable object had been stolen by the reportedly Fallen Angels but his spies managed to pry more information and it was rather a dozen of rogue priests, paladins and Templars working with the Grigori to steal this object, an Excalibur.

"An?"

"Yes, my lord. Apparently the original Excalibur that Arthur Pendragon possessed was shattered into seven shards and this missing sword is one of them. I can send a brief document of these artifacts to you if you want so."

"Hmm, the timing is too perfect. But to be sure, monitor them for the time being. We cannot act rashly lest our entire effort would be a meaningless. Tell Apollyon to postpone the hunt for those Khaos Brigade insects and gather Sigurd, Corax, Cerberius, Julius and the rest of the captains to gather at Kuoh City as soon as they can. No need to rush but alert them as I said."

"Understood my lord." And Ludger cut off the connection. Kagami knew that their conversation had been eavesdropped from the beginning but well, what's good for being too secrecy? As expected, the Sitri and Gremory heiresses were indeed doing so and they were mortified to hear the dreaded names. The latter reached her brother to inform him of this matter.

The next days were relatively normal for Kagami except the wary eyes of the aforementioned Devils and other creatures in Kuoh Academy. Today was supposed to be Apollyon and Sigurd's arrival, the others were delayed a little but he didn't mind. He was watering the flowers in the school's neat little garden, it reminded him of Beelzebub when he was still alive. His general had a soft spot for plants and as his master, it was his responsibility to honor it. And then he noticed a spike of power in the abandoned building so he abruptly stopped the activity and headed to it, hoping to see something interesting amidst the boring world of humans.

Indeed it was.

"I have told you for a million time already. I will not accept this marriage –"

"Kaichou, we have an intruder." How cruel his luck was. The door snapped open and revealed the short white haired girl from before, he believed she was a youkai or a nekomata judging from her unique Senjutsu, and the ones knowing him reeled back in shock, even a maid he recognized from that time.

"K-Kagami-san, what are you doing here?!"

"Oh, what is this puny human doing here?" A delinquent-looking blonde young man spoke in his arrogant tone. Satan saw red as he lunged forward and delivered a folded hand thrust directly at the blonde brat's heart.

"Do. Not. Equate. Me. With those monkeys!" Kagami snarled as he twisted his hand, which pierced through the man's body to the other side. Despite clouded in rage, he was conscious enough to catch a hand from the maid with inhuman speed, much to her surprise.

"Y-You…bas…tard…"

"Release lord Phenex at once, human!"

The maid demanded before finding her levitated in the air by a hand choking her throat. As if an instinct, his two newly arrived generals warped into the room. Apollyon leveled his dual 'bolt' magnums while Sigurd summoned the shining Bolverk Gram. The tension was so high that the lesser Devils felt like the air was frozen.

It took Rias a lot of efforts to persuade Kagami to release both Riser Phenex, the irritating blonde, and the maid, a Lucifuge if he wasn't wrong. Sigurd immediately berated him for letting his temper get the hold at him. Despite a sizable hole on his chest, Riser managed to laugh. He was greeted by a bolter blowing off his right leg.

"Shut up, worm." Apollyon coldly stated. Grayfia still could not recover from the shock that the Lord of Locusts was here in the same room with her. It was a common knowledge in the Civil War that the Lucifuge was a supporter for the Old-Satan Faction and it costed their clan severely. When the Alpha Legion entered the fray, it was Apollyon who hunted down her entire family and massacred them all except Grayfia and her brother, Euclid as they were defecting from the Faction anyway.

"Do you understand now, my lord? You cannot let the others laugh at us, the Alpha Legion, just because you can't control your anger."

"I know it, alright! Still regret that I didn't blow the brat into the sun though."

"My Lord, that attitude again!"

…

Rias gave Kagami and his subordinates a summary of what happened and the King of Ruin laughed it off. Riser wanted to relent so much but the icy gaze of Sigurd completely froze him.

"I thought it was something interesting, turned out it's a really good joke!"

"Damn it, Kagami. Buchou's life is at stake here!"

"Silence, boy. Don't interrupt my lord." Apollyon said, silencing the boy. Kagami slapped his general's back playfully.

"Nah just let him speak! I find it amusing to see a human-turned Devil boasting about woman's private sections and all. The kid wants to take his master's virginity of all things! Gahahahaha!"

Rias was embarrassed at the statement while Issei huffed his chest with pride. Kiba facepalmed and Koneko just munched her snacks in ignorance. Akeno, in other hand, was eying Kagami with lustful eyes. She had been interested in this new guy lately and his performance today boosted it to new level. Kagami shuddered at the feeling of something is looking at him uncomfortably.

To regain his authority, Riser summoned his Peerage full of girls and boasted about their strengths. He suggested a Rating Game between him and Rias with the winner would decide the outcome of the arranged marriage, which earned the agreement from Grayfia. They traded glares with each other before Riser left with his Peerage, having agreed on letting Rias ten days to prepare.

"So Apollyon, what is this whole 'Peerage' and 'Rating Game' things again? I didn't pay much attention back when she explained it to us."

"I believe a Peerage is somewhat similar to us Legion, using chest pieces to measure one's ranking. The Devils have been using this for quite a time now to increase their numbers by resurrecting humans with exceptional powers as Devils." This brought a scowl on Kagami's face. "And a Rating Game is a match between two or sometimes multiple Peerages. Think of it like a soccer match."

"I see. Well, this is not our business anyway." Satanael stated. And then he looked at Rias. "But you know what? I am dead boring here and I thought I could entertain myself for the time being. Gremory, I and my generals will volunteer to train your, what was that again? Peerage. What about you two, Apollyon? Sigurd?"

"We have no objections, my lord." They said in unison. Rias was puzzled but still thanked them. Issei didn't get why this Alpha Legion was so feared by that 'grilled chicken', the 'hot maid' and his Buchou. Here came Sigurd and his flashy spectacles for lessoning.

"Do you understand now, Mr. Hyoudou?"

"I… Err… So basically, this Alpha Legion thingy is Kagami's Peerage? And I still don't understand why you guys get those two scared as fuck."

"Because they are the personal guards of the King of Ruin." Rias said, locking eyes with Kagami. "Isn't that correct, Lord Satan?"

"Hah! I expect no less from the sister of the current Lucifer. Even though your power is pitifully weak, I still grant the privilege to be trained by me and my Legion."

Rias' Peerage didn't recover from their shock as Sigurd. made a good point at telling them to keep a secret as Satan, despite his return during the Civil War, hadn't revealed himself truly to the worlds. Apollyon was checking the status of each member of the Peerage and measured their abilities.

"My lord, they consist of two magic users, a melee and agile fighter, a mix of both and a questionable between two." He pointed at Issei, who was then shut up by his stare. Kagami rested his chin on his folded hands and thought.

"Call for Julius, he can teach the nekomata, and Cerberius. I hope the latter can whip something into that pervert." And then he stood up. "Gentlemen, we leave now. Make sure you get the proper equipment, Gremory, as I and my generals are strict instructors. I don't like it when I put my time and effort into something that turns out to be a waste, not at all."

Satan and his Legion will still be part of the canon plot but they mostly stay in the sideline and handle the other matters such as the Khaos Brigade. And yes, I use a lot of Warhammer 40k's elements in this fics.