The halls of the Tepes castle kept such stillness that even the frigid air felt bothersome and stale against the skin, making anyone that dared to get inside feel more on edge. More alert, even. But the creeping sensation of something being terribly gone didn't disappear that easily. It might not be the main manor, the place with the most people with power and influence, but it still lacked the common tells of life. And that made people acutely uncomfortable.

No vermin, no bugs, not even a single bat that got woken up by the intrusion and light of Fate Weaver's group. Not a single soul in sight. It almost felt sterile, like a hospital. No things, not even dust.

"I don't like this." Murayama Shino murmured, stance ready for battle. But easily exploitable in case of a double fake out. To the side and above, or maybe from below and behind…

"Don't worry! Keep your eyes open and stay close. It's always better to not have to fight, after all." In spite of her carefree way of walking, Shidou Irina had no openings whatsoever. The small movements she did without thinking spoke of a seasoned warrior, one that knew what to expect of her surroundings even without having mapped them ahead.

A juicy, knowledgeable warrior with years of fighting under her belt…

"Irina's right." Fate Weaver had his sword Boosted Gear ready, using its emerald crystal-like blade as a form of lighting. It didn't brighten up that much, but none of them seemed to need that extra visibility. He, at least, walked and spoke with his face turned. Not looking ahead "It's bothersome when bad guys send low-level grunts before facing you, so this is a nice change of pace."

A fake opening. He'd be able to parry any blow that didn't take him off his feet, and even if something big enough managed to land a hit, it'd be very eyebrow-raising that something like that appeared out of nowhere.

The trio kept moving, opening doors and finding nothing of value on the first floor of the castle. Basically wasting time, but their diligence in looking for secret passages and hidden rooms where they could be ambushed from couldn't hurt them. They had time, or so they thought, so even if they wanted to hurry they didn't.

In the dark corners and recess between bricks and furniture, Stain stalked their advance. Noting their concentration, their field of vision, the way the environment made them move. The slime followed their patterns and waited, knowing full well that it wouldn't be able to fight the Red Dragon Emperor with its current biomass.

The creature had prepared this place for them, slowly assimilating the few vampires that the Khaos Brigade had left… Unaugmented. The rest of them, those who had been tainted and transformed into lesser Evil Dragons, slept placidly several meters below ground. Sealed away by magic and rituals that Stain had been there to use and place to begin with. With its assimilated Khaos Brigade workers.

The creature took advantage of how much the lower levels of the power pyramid actually did, how they had to be everywhere carrying out orders and doing the dirty work for those above. Those who were too confident in their power to actually bother making things work. Miyuzuin Yaegaki-Belial understood this, and had continued the Lord's work in his absence. Following Stain close, not letting the creature have the same freedom to satiate its hunger as much as it wanted: She hated it, but couldn't help finding the slime useful. The Lord had been content to let Stain do as it pleased as long as it wasn't discovered, and as long as it didn't endanger him.

It thought that, with time, it'd find a gap to finally assimilate the Lord. But everyone always made sure to keep Stain busy, and it knew better than anyone that it would only get a single chance at trying. So it waited, faked trying. It kept close to the devils in the form of birds and small critters. It did as commanded.

While waiting for Fate Weaver, Shidou Irina, and Murayama Shino to advance, Stain mined the secret minerals found in another corner of the world; filled with magical energy to fuel the golems that it was also helping build. It infiltrated secret circles, understood rituals, and traded in goods that it had also packed and hijacked. Its many bodies worked, and Stain absorbed all the information, made every choice, and put a pin on the bigger picture. On that which the Lord wanted to see. It didn't use its newfound demonic power like the rest, but fueled its mental connection to every piece of itself and created biomass to use it all instead. Stain, the Gate, was alive in a way that no one else would ever be… But at the same time, it knew nothing of life. Only being able to mimic and interpret the knowledge and experience it took for itself.

By the time the three infiltrators got to the next level of the castle, Stain had already prepared everything that would happen within.

"...!" Fate Weaver's senses screamed at him to stop, and he lifted a hand to signal the others to cease walking.

Shidou Irina had sensed it too, perhaps even sooner than Fate Weaver. So it left Maruyama Shino to heed the signal and get ready to battle.

Stain's corpse-like bodies crawled on the floor, eyeless and releasing biomass twisted into looking like blood and viscera. Not an illusion like the nekomata Kuroka used, but twisted Stain-body parts that behaved like the real deal.

"Hun-gry… So… Hungry…"

"Please…"

"I'm sorry… I'm sorry…"

"My daughter… I didn't… No…"

The revulsion came instantly, seeing 'people' in such a sorry state, some missing their entire lower section, some parts in gruesome ways, could only be ignored if the individuals had certain mental parameters that none of them fell within. They had to stop themselves from releasing the content of their stomach, and so Stain was able to shift its hidden mass without being noticed. It followed them, hiding amidst their biological reactions. The moments they were the most vulnerable.

It felt nothing toward them, so no instincts kicked in. It knew them only as food, but Stain was intelligent enough to not try to hunt them. So they didn't react to the creature's predatory sight.

"Dear God…" Shidou Irina murmured without thinking.

"Ow!" Maruyama Shino cradled her head.

"Let's dispatch them quickly." Fate Weaver turned his sword around, facial features twisting with determination "Something really awful happened here. And I'm going to figure out what."

Stain turned its corpse-like bodies as they spoke, mimicking being alerted by their voices.

"AH!"

They crawled faster, some even springing bat-like wings from random parts of their bodies, others growing bat heads on shoulders, the back of their heads, or even on their hands. The nature of their transformation was hand-picked for added horror, only looking random in how no one seemed to have the same mutations.

Shidou Irina activated a form of power, and steampunk-like wings extended from her back. Shining silver with copper outlines, and radiating enough holy energy that Stain had to suppress its new devil instincts of running away from it.

It knew what that was. Artificial Ascension, the Sacred Gear 'Mechanical Angel'. According to the Lord, this woman should not have such a weapon. But one of Excalibur's fragments instead. Like quite some of his assumptions, this information was wrong. But Stain had been ready for unexpected situations. It hadn't just lured them all into the castle. It had been the annoying brat that gave Fate Weaver ominous directions, the kind elderly woman Shidou Irina helped cross the street when they arrived at the country, the host in the hotel that Fate Weaver and Maruyama Shino had had sexual intercourse in.

Its mission, as the creature understood it, involved creating the perfect opportunity for the Lord to get information on the Sephiroth Graal, and this whole 'invader' business. The latter seemed to refer to the Lord in particular, but Fate Weaver also reacted badly to this mysterious word. And while Stain hadn't found much in that department, it did know that getting Fate Weaver into this castle would help with the first point in its mission.

On the upper levels of the castle, guarded by two Evil Dragon clones made out of vampires, a whole ritual of sealing held the body of Valerie Tepes. She, as the Lord explained, had one of the pieces of the Sephiroth Graal, but Stain lacked the power to break her out of it. It'd lose control of its bodies, and that'd create others like itself. The Lord did not want more slimes, and Stain did not want to give up the knowledge and memories that it'd lose once those others spawned.

So it brought Fate Weaver here, it led him and his companions through fake trials and tribulations, and led them to a false sense of security. It disguised itself as an important vampire by using pieces of appearances it had acquired, and gave them a bombastic speech that forced both Shidou Irina and Fate Weaver into combat.

Stain couldn't take them both, but it didn't need to. It faked using a drug to twist and transform into an Evil Dragon, and used another body to lure one of the guards to Valerie Tepes' room toward the battle. It swapped places by using a bit of demonic magic, and continued to create bodies to add to the danger.

When that Evil Dragon died, Fate Weaver got fed up and slammed through brick and concrete toward the top.

Stain had already moved the other Evil Dragon there, and attached itself to it to create a different appearance. The slime had been there when the transformed vampire had been given this role, so it remained docile. It, like its twin, didn't have enough power to break through the seal. But that didn't matter. Fate Weaver got into Balance Breaker mode and took the dragon head on while Shidou Irina and Maruyama Shino took to the sky.

In another part of the world, Stain approached Bel Lucifer and informed her of Fate Weaver's secret mission. That she, perhaps, could 'test him' if she hurried.

The creature moved to Valerie Tepes' room, hiding biomass wherever possible to snatch her from the three infiltrators the moment that the Heavenly Dragons started fighting.

Diodora got in trouble.

"What do you mean you've been hosting a high-level Stray Devil in this town all this time?!" Rias yelled while Diodora and Genshirou held one of Kuroka's hands on their own. They had tried to make her leave, but she had none of that. So… This "What if she had hurt anyone?"

"If I wanted to hurt people, I'd have done so already. Meow." Kuroka pointed out, shaking off each of the guys' hands to get back to cuddling her little sister "I've been here for two years, meow! I'm no threat!"

"Two whole years…?" Rias looked like she didn't want to believe it.

"Yeah." Yuuto nodded, making his leader turn to face him.

"You knew?"

"Not precisely… It was weird how Koneko-chan sometimes disappeared for long periods of time, and when we were watching over Diodora-san it also happened… I just figured they had some secret that Koneko-chan kept while he was gone." The blond had the gall to smile awkwardly, but didn't apologize or offer a solution. He had looked deep in thought when Diodora met the peerage, but now he had a distraction from his thoughts.

Probably the Sacred Gear thing, but Diodora wouldn't breach the topic just yet.

"Really? I mean, Koneko-chan is in that age after all. It could've been anything." Akeno cradled her cheek, looking concerned in that not-really-real-but-real-enough way some comedies use.

"Am I the only one concerned about this?" Rias looked ready to panic, but her peerage didn't share the feeling.

"I have no clue what's happening." Loup replied.

"I can see lifeforce, I knew she was here since the beginning." Benia added.

"If Diodora-sama brought her, there has to be a very good reason… Right?" Akeno's threatening undertone didn't escape Diodora's attention.

"Well, yes. I assume you all have questions for me, and I wanted to talk to you about my… Situation." Read: Tell them his side of how he got involved with the Khaos Brigade before Fate Weaver came back and ruined it by pointing out how the original Diodora's actions made more sense "And Kuroka is a part of it, so I thought it'd be a good idea to start with this."

"She'll be joining our peerage." Miyuzuin added, being to Diodora's side in case he lost his balance "Lord Diodora already sent the proper message to the Demon Lords to get back his Evil Pieces, so there's that too."

Koneko blinked a couple of times.

"You're not a reincarnated devil."

"Lord Diodora doesn't have his pieces yet." Miyuzuin pointed out "From now on, I'll function as his Queen… I suppose I should ask you to take care of me."

The devils still looked somewhat confused, maybe reluctant to process everything at once.

It didn't matter, Diodora had time to explain.