A Sound Deal

Aunty hadn't been surprised.

That thought kept turning over and over in Sona's head as she and Rias' Peerage waited for news.

"She's lying," Issei denied, pacing back and forth in agitation. "Senpai isn't like Diod... Senpai wouldn't work with Chaos Brigade. She has to be lying. I won't believe her, no matter how magnificent her Oppai!"

"Ise," Asia said worriedly, placing a hand on his arm to try and calm him down. 

Mikasa Ackerman wasn't the most expressive of women, but those she cared about deeply learned her tells over time. Those expressions that did slip through conveyed a world of meaning.

And, hearing that the boy she loved was being accused of leading an inter-pantheon terrorist organization bent on sowing chaos, Mikasa had not been surprised.

Like a song on repeat, Sona turned the memory over and over in her mind.

She was trying to make sense of this mess. 

Trying to grasp onto anything, anything at all, which would let her understand what was happening.

Trying to find anything that would be a valid argument against Kuroka's claim that Eren was secretly in control of the Chaos Brigade.

That he hadn't been the one to help found it.

That the boy she had seen, talked to almost daily and come to care about wasn't secretly the leader of monsters. Monsters like Loki, like the Old Satan Faction, like Diodora Astaroth.

Sona was trying to find any way to prove that this last year and a half had not just been a lie. That Eren hadn't been using them, stealing information from the sisters of the Satans to further his own goals.

Only... Mikasa had not been surprised.

"Senpai..." Kiba stared at the ground with a dark look on his face. "Senapi's always had a dark side. He told us about it before. We just... never saw it."

"That doesn't mean he's a bad guy!" Issei denied strongly. "He's just... He might have done bad stuff before, but he regrets it. He's better now. The Senpai I know isn't a bad person."

Mikasa's only concern was with his revealed capabilities. 

Like she had already thrown away every moment of care and love they had shared and Eren was now an enemy that needed to be fought.

Like Eren had always been her enemy.

She had accepted Kuroka's accusation as fact right away.

Like it made perfect sense for the weak, sickly human who talked with them, counselled them, cared about them, and laughed with them was secretly... Something else.

Someone else.

Had they ever known Eren Yeager? 

Truly known him?

Understood him?

"Ise," Xenovia joined Asia in trying to reassure their lover. It was the gentlest anyone there had ever seen her. "You only knew a part of him." 

Issei looked at her, hurt. 

Xenovia pressed on. 

"Eren Yeager did not become the 'Child of Evil' by kind deeds. He's killed hundreds. Maybe thousands."

"But," Issei floundered, trying to connect the boy who helped him with the Child of Evil Xenovia talked about. "But he was a soldier, right? A mercenary? He only killed bad guys, right?"

"I do not know of any indiscriminate slaughters, and most of his victims were probably enemy soldiers," Xenovia allowed, and Issei looked hopeful. "But not all."

The more Sona thought about it, the more she tried to find proof against Kuroka's claims, the more she found the opposite.

From the first day, it had been clear Eren had been hiding things. 

Initially, it had seemed he had been a blind and scared youth, traumatized by his experience as a child soldier and looking to pass his last days in peace. She had thought he was hiding the fact that he had been a mercenary, unaware that they had been able to investigate him.

But that was only the first of what seemed like innumerable layers of secrets and mysteries. Whenever they peeled back one layer, believed they had understood Eren, thought they knew his depths, they discovered a deeper abyss.

Then, with the revelation that he knew about magic and wasn't blind, he kept secrets of his original world—secrets he and Mikasa had shared between themselves that they were so hesitant to discuss.

Another layer, another mystery.

Had Eren asked Mikasa to tell Sona about their world because he didn't feel it was right for him to explain, or had that been another lie, a way to put off a conversation until he betrayed them? It wouldn't matter what they learned then, would it?

Had it all been a distraction so they wouldn't ask about his time in this world?

"There are no good guys," Akeno said softly as she ran her hand through Koneko's hair as the Rook hugged Rias tightly. 

The nekoshou had been clinging to their King ever since they had teleported to this waiting room while the Satans talked with Kuroka and Mikasa. Kuroka hadn't been opposed to them following, but Aunty had tried to push back.

To no avail, of course. They refused to be sidelined for something like this.

"Eren fought for warlords, in civil wars, or as an insurgent. Even if he only killed enemies, others would be presganged to join either his side or the other. Women. Children." Xenovia did not look like she took any pleasure in her words, though she said them with certainty. "Even without accidents, Eren fought for despots and other military strongmen. And there were accidents. If not from him, then from others on his side. People he helped went on to do terrible things, even if he didn't do them himself."

For an instant, Sona grasped onto the fact that she and Rias had their familiars watching Eren most of the time.

Surely, they would have caught suspicious activity at least once over the year and a half?

Then Sona realized that if Eren was as accomplished with Senjutsu as Kuroka claimed, it would have been pathetically easy for him to not only sense their familiars watching but also slip by and deceive them to keep in contact with his subordinates in the Brigade.

After all, he had managed to slip off the heavily warded Gremory vacation island without issue. None of the Gremory servants found traces of him having been there when they went to clean it.

"That church he destroyed? I don't know if the men he locked in there were slavers or not," Xenovia said grimly. "All I know is that a nine-year-old boy locked seven men in a church. He listened to them scream and beg for their lives as he placed explosives. Then, while my guardian bled out, he blew it up and left her to die. She told me he didn't even blink. Whether they were bad men or not, nobody who kills people that easily, that cruelly, without feeling anything is a good man."

Issei looked away, unable to meet his lover's eyes.

'Be careful with Eren Yeager. You have no idea who he is. What he's capable of.'

Suddenly, Sona felt so foolish. So very dumb. Immature. Childish.

She, a teenage girl, had let her feelings blind her to the holes in Eren's story.

How had a human child managed to defeat Griselda Quarta? One of the church's top exorcists would certainly not have been taken down easily, even if taken by surprise.

How had Eren known so much about the supernatural world when he said he tried to avoid it?

How had Eren, only seventeen years old at the time, had enough Ki to rival an Ultimate Class devil in power?

Not once had she tried to poke holes in his story, content to let him keep his secrets.

Sona hadn't challenged him at all, not once.

Because she had loved him.

'He'll break your heart.'

"But-but, he's better now, right?" Issei asked, looking around the room hopefully. Desperately. "He did those things to survive, but he doesn't have to anymore, right? He regrets it and is better now, right?"

"Eren..." Akeno trailed off before shaking her head. "Even if he did regret his actions, he'd still do them if he thought they were necessary. He'd still move forward. That's the type of man he is."

Mikasa hadn't been surprised. 

Because, to her, it was expected.

Self-loathing filled Sona.

Why had she not heeded her aunt's warning? Or at least been better prepared for something like this?

Clearly, her Mikasa had concerns about Eren, even from the first day of meeting him again. Sona doubted she knew precisely what was going on with Eren, but she still was preparing herself. Mikasa had tried warning them in her own way, lacking as she no doubt had been in the detail department.

Mikasa had never had anything but their best intentions at heart, and they ignored her.

"Love. Always love. But never let love be chains."

Mikasa's feelings for Eren were real, and Sona was still certain of that, but her aunt had not let them blind her. 

Why had Sona allowed hers to do the same?

Sona knew why.

Jealousy and pride.

And all they got Sona was this tearing, ripping, gut-wrenching pain in her heart.

"Why," Issei asked, looking around the room at the sad, pained, angry faces. Tears of frustration and pain started to bead his eyes, and he rubbed them furiously. "Why is everyone accepting this? Why do you think Senpai can do this? He is our friend. We need to believe in him!"

"It is because he is our friend that we know Eren," Rias said hollowly, arms tightening around Koneko. "I... I think if Eren had a reason, a strong reason, one he believed in and was willing to fight for, then he could do anything. No matter how much he'd regret it, he'd still keep advancing. Even if it meant becoming a monster."

"But why," Issei pleaded with his King. "What reason could Senpai have?"

"...I don't know."

"Um," a hesitant voice asked in the silence after Rias' despairing whisper. 

All eyes, even Sona's, looked at Rossweiss. The newly reincarnated Pawn shifted uncomfortably at the attention.

"I... I don't know this Eren Yeager," the Valkyrie said, still new to the group and more than a few years older than those present. She was still trying to fit in. "But I think we need to know how he did it before we can ask why."

"What do you mean," Sona asked, seizing on any subject change. 

Anything to distract her from the ache in her chest.

"Well, if that woman is right," Rossweiss nodded toward the room where Kuroka was still talking to the Satans. "He is the leader of the Chaos Brigade. He helped build it. According to every report I've read on the Brigade, they oppose the Peace Treaty and have formed with the Ouroboros as a figurehead. Apart from that, it's just a bunch of factions agreeing to stay out of each other's way for their goals."

"That is the common consensus, yes," Sona nodded quickly, glad to have the distraction from her spiralling thoughts. "We know a few factions by name. The Old Satans are the ones we've dealt with for the most part, as they target devils, but we also know of a faction of magicians from the attack on the school, Nilrem, and the Hero Faction. They claim to be the leading faction, but we can't say for certain. We don't know if there is still a Norse faction without Loki, but we can assume any number of other factions from other pantheons that are dissatisfied with the Peace Treaty."

"That is what I am talking about," Rossweiss said, gaining more confidence. "How is a human the leader of all that? If it is this Eren, then how did he do it? Loki said he wouldn't act on the plan of a dead man, which meant that while he thought the leader was alive, he was following their plan. How do you get so many factions, many with competing interests, to follow your plan? Not even the God of the Bible could do that, but a human could?"

"He has that sage stuff, right," Issei guessed. "If the nekomimi is right, then Senpai's super strong. Did he just beat them up?"

Despite his reluctance to believe Eren was their enemy, Issei looked almost excited at the idea that Eren was secretly a badass.

"All Senjutsu does is enhance what is already there," the Pawn disagreed. Rossweiss was a prodigy in magic, Sona remembered. She probably knew more about the subject than all of them except Kuroka. "Usually only existing Ki abilities. And even then, it's usually just physical abilities. Sages are rare, but even the most powerful could never fight gods except for a few who combined it with other abilities. Taoist spells or Youjutsu techniques. And even then, none of it reached the level of a properly trained Longinus user, let alone a god. So how did a human sage manage that if he has no magic or Sacred Gear?"

Rossweiss looked around the room. Realizing everyone was watching her as she lost herself in one of her favourite topics, the Valkyrie shrank back in on herself slightly.

 "I just thought that if we knew how he did it, maybe we can figure out why."

"My aunt knows," Sona said softly.

"That 'Warhammer' thing?" Rias asked, and Sona nodded. "I don't understand. They said their world didn't have magic. Or any supernatural races. Even if... Eren was lying," Rias swallowed the words like her throat was stuck. "Aunty wouldn't go along with it."

"It could be a title," Akeno suggested. "We've never really seen Eren fight. If he's anything like Aunty, he could be very strong as a human... if he was healthy, I guess. Can any of you imagine Lady Mikasa as a Sage?"

Sona suppressed a shiver at the thought.

Her aunt lacked any magic or demonic power of her own, but thanks to sheer skill and speed, she could fight well above her weight class. With the right weapon, she could even kill Ultimate Class devils.

If she had Touki, let alone Senjutsu, Mikasa Ackerman would be an Ultimate Class devil easily.

If Eren could fight as well as she did and was as talented with Senjutsu as Kuroka claimed, he would definitely be an Ultimate Class threat.

"Eren 'Warhammer' Yeager," Yuuto tasted the words on his lips with a sardonic smile. "It isn't bad."

"It isn't a title," Mikasa said plainly as the sealed doors opened.

Everyone rose to their feet to look at the group that emerged. It was unsurprising that they could hear what the young devils had been speaking about from inside.

Sona noted that her aunt's was a mask of neutrality that didn't let anything pass.

Serafall, on the other hand, looked between Sona and Mikasa worriedly, biting her lower lip and twirling her hands awkwardly.

The other Satans, Sirzechs Lucifer and Adjuka Beelzebub, looked grim but resolute.

Falbium Asmodeus was nowhere to be seen.

Kuroka was all smiles, in contrast to everyone else's mood.

"So," Issei asked eagerly, not caring about propriety in the slightest and more concerned about his missing Senpai. "What's happening? Where's Senpai?"

"We don't know. Agents are going to the headquarters Kuroka told us about, but they are probably already abandoned. For now," Sirzechs said with a tight smile. "Eren Yeager will be listed as wanted, with orders to be captured alive, if possible."

"Why!"

"Issei!" Rias barked as the Red Dragon Emperor stepped toward the Satan's aggressively.

Issei bit his teeth but backed down.

"If it makes you feel better," Sirzech said, giving the boy a pained smile. "I don't think we can capture him."

What sort of power did Eren have that not even the Satans, with all the resources of the Underworld at their command, didn't think they could capture him?

"You really believe he is the leader of the Chaos Brigade," Sona asked, her eyes looking from her distressed sister to her placid aunt.

"He is," Mikasa answered simply.

"Mi-chan," Serafall looked at her Pawn sorrowfully.

"Eren will do what he thinks he needs to," Mikasa said. 

Her voice was empty of all emotions. 

Not cold. Just empty. 

"He always has."

"What about her," Rias asked, looking at Kuroka with narrowed eyes. "What's going to happen to her?"

"That will depend on whether the information she provides is accurate," Sirzech explained.

"Onee-sama is a good kitty nyaow!"

"We shall see," Beelzebub said. "Falbium is already verifying your words."

Sona blinked in shock.

Something had gotten the infamously lazy Satan Asmodeus to do work? And instead of just sending subordinates to do it for him, he went himself?

What in the Underworld had Kuroka said in that room?

"For now," Sirzechs said with a sympathetic smile at Rias. "May we speak with Koneko?"

"What for," Rias asked warily, standing between the young Rook and the Satans.

"It is nothing bad," Sirzechs explained gently, not showing if his sister's caution had hurt him. "Before we can decide what to do with Kuroka, we need to know if she is guilty, and Kuroka said Koneko has the proof she is innocent."

"And you believe her?" Rias demanded angrily, stepping forward in a mirror of Issei's earlier action. "I am not going to let her hurt Koneko again!"

"...Buchou," Koneko held her King by the back of her shirt. 

Rias looked back at the Rook, and Koneko gave her a small shake of her head. Rias still watched Kuroka like a hawk as she stepped aside. Not far enough to be out of Koneko's reach, though.

"I need to know," Koneko asked with narrowed eyes at her sister. "Did Eren go mad because of Senjutsu?"

Kuroka blinked in surprise, then her gaze softened, and she crouched down until she was at eye level with the smaller girl. 

"No Shirone. Senjutsu cannot make someone mad unless they have a really weak mind. Both me and Eren are sane."

In a rare moment of anger, Sona wanted to shake the cat girl by the neck and demand to know what part of 'destroying the Underworld' was sane.

She didn't though. She understood why Koneko asked that question.

It would be so easy if Eren simply went mad due to his Senjutsu. 

If exposure to the malicious Ki of the world had driven him mad, then he hadn't betrayed them. 

Hadn't betrayed her.

But Sona could not bring herself to believe such a convenient fantasy.

Because Mikasa had not been surprised.

Kokeno stared into her older sister's eyes, looking for any lie.

Then she looked at Sirzechs Lucifer.

"...What do I need to do?"

"We just need to see your hairpin for a moment," Sirzechs said.

Koneko's brow furrowed as she raised her hand to the cat-shaped hairpin that kept her silver hair from her eyes.

"Why do you want it," Rias asked defensively. "It's all she has of her mother."

"We're not going to destroy it," Sirzechs reassured. "You'll get it back."

Koneko hesitantly took the clip out of her hair and handed it over.

Lucifer took it gently, not saying anything about the girl's trembling hands, and passed it to Beelzebub.

A magic circle lit up below the clip and enveloped it.

Beelzebub's eyes narrowed in thought.

"It's a device used to record information. Like a human hard drive, only it doesn't just contain documents and footage, but also spell formula."

"Can you tell what is in it?"

"It will take me days to go through all of it," Beelzebub told his friend. "But I can give a general summary right now. It is a copy of illegal research conducted by the Nebiros clan on how to create Artificial Super Devils."

Sona's eyes widened.

The Nebiros clan was a clan of Extra Devils famous as the last surviving of the Six Houses of Lucifer. All the others had either died in the Great War or joined the opposing side of the Civil War.

The sole exception was the last surviving member of the Lucifuge family, who married Sirzechs Gremory.

They were also a branch family of the Naberius house.

More recently, however, the Naberius clan was more well known for being the noble house involved in the Nekomata Incident, where a promising bishop was said to have gone mad with her power, killing her master and devolving into one of the most dangerous Stray Devils ever to exist, Black Cat Kuroka.

"While this is not a record from her master," Beelzebub continued, nodding toward Kuroka, whose eyes remained locked on Koneko. "It does mention the branch house he was a part of being included in the research and has extensive notes on experiments on nekomata. Their mother, Fujimai, in particular, was a major subject. Senjutsu was a significant study target, and the experiments were... not gentle. It corroborates her story."

"This is going to be a disaster," Sirzechs sighed, rubbing his face tiredly. "Get everything you can out of that and make sure you don't destroy it. I'll deal with the Naberius."

"What does this mean?" Rias asked her brother.

"According to the law, any King who violates the law loses the right to their Evil Pieces. And those Pieces are within their rights to defend themselves from said King," Sirzechs explained. "It was one of the first laws we put in to protect reincarnated devils. If the Nebiros Clan were indeed conducting experiments on nekomata, which it looks like they were, and the Naberius continued those experiments later, then she was within her rights to kill her King. Which means she is, legally, innocent and no longer a Stray Devil."

"The Naberius clan can lose their Pillar status over this," Sona said with narrowed eyes, realizing the larger implications of this revelation.

"If we can prove it and it's not scapegoated onto one member. They will either become an extra devil clan or lose clan status altogether, depending on how pervasive the experiments were among the family. Or it will push them to join the Chaos Brigade."

There was a whole mess of political intrigue there, one Sona was unwilling and unable to deal with at the moment.

For the first time in her life, Sona decided to be like her sister and leave that work to Sirzechs and not think about it.

"But," Rias protested, pointing toward Kuroka. "Even if she's not a Stray, she is, or was, part of Chaos Brigade. She's still a criminal."

"We've struck a deal with her," Serafall said, not taking her eyes off her Pawn. "Now that her innocence in her original crime has been proven, or at least has reasonable doubt, we can pardon her in exchange for information. Information we need."

All three Satans looked grim at the reminder, but Kuroka simply continued to smile gently at Koneko, who was staring at the elder nekomata in shock.

"For now, as part of that deal, she will remain under observation by Mi-chan- Er, Mikasa," Sirzechs stumbled but continued affably. "Also part of that deal was that she was allowed to live with, or near, her sister, so she will be staying in Kuoh. Between Mikasa, Azazel, and both your Peerages, she won't have much freedom."

"And it keeps her out of the Underworld," Sona said, with a note of accusation. "She can't spy on things from Kuoh."

The Satans gave her a wane smile but nodded in affirmation.

Sona had two other realizations that she didn't vocalize to the group.

First, by keeping Kuroka near Koneko, they were indirectly using the Rook as a hostage for good behaviour.

Second, Eren had already shown an interest in Kuoh and them in particular. With Kuroka there, they kept all his known associates in one place, which might lure him out.

Sona was certain that Kuoh was about to have dozens of Ultimate Class devils hidden nearby, just in case.

A year ago, the thought would have made her angry.

Now, she just didn't care about the blow to her pride.

Sona was just tired.

"I'm sorry I wasn't there, Shirone," Kuroka said softly, looking into her sister's eyes. "But I'm going to be there now. Even if you don't forgive me, I promise I will prove you can count on me. I will spend every day for the rest of my life proving myself if that's what it takes."

Sona couldn't even begin to understand what the young Rook felt at that moment. Rias clearly wasn't happy.

But Sona?

Sona wasn't happy either, but she could see the silver lining. With Kuroka at hand, she could get more answers.

Both Kuroka and Mikasa owed them that.