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Shinobu was tired at this point. Restless. Enough to do things she wouldn't have done before, when she was younger. Though that had been true for some time.
Her emotions were things she reigned in on the daily, in so many contexts. While fighting. While talking with others. While in her lab. Always present, intensely so- and she had learned how to suppress them, how to roll them up into a tight little ball in her chest and tuck them away in order to maintain the fragile sense of control she needed to perform in life. She could determine her own actions, she knew, and that was it. Bottling her feelings was her way of proving that to herself.
But for all the good it did her there were repercussions, mostly in that the build-up of anger and frustration had to be relieved somehow. In fighting, mostly, with a smile plastered on her face all the while, but this night had been different because she was at home taking a break Kagaya-sama had forced upon her and she had nowhere to direct her rage.
Well. She did, she remembered, have a test subject at her mercy.
Shinobu despised demons. That much was clear, as most demon slayers did- one didn't exactly pledge their life to eradicating them if they didn't harbor at least some amount of dislike. But what she felt towards them was something more. Her hate consumed her life, ever since Kanae had been taken from her, and even the thought of all the hell demons had brought to humans made something inside her burn. It fueled her every action. The only reason she was still able to function as a person was because she'd made a promise to Kanae, that she'd avenge her death and protect others from the monsters who'd stolen her life. One step in that process was acquiring an examinee or two - demons, trapped and chained in the cellars of the Butterfly mansion under the pretense of being questioned and assessed.
Kagaya-Sama had allowed this particular endeavor of hers under the condition that any captured demons were not to be harmed, only granted a merciful death after any necessary procedures aiming to discover more about their nature and aid the Demon Slayer Corps’ quest. He called them subjects. Shinobu called them lab rats.
In private, that is. She kept her experiments to herself.
Most were aiming to gather information around Wisteria and the effects it had on demons. She'd done tests like this before, of course, in order to develop the signature poison she'd been using for what felt like years now- but those instances were all out in the field, performed in battle. Not until she was able to confine a demon was Shinobu really able to hone in on each detail of it. How much poison it took to irritate a demon. To wound it. To kill it. Whether the effects would dissipate over time, and exactly how long. In the cells under her lab, she could note the effects drop by drop.
All this to say, her test subjects were usually just that- test subjects. But this night Shinobu was overwhelmed, consumed by emotion, and with a being she hated so passionately just tucked away under her control where else was her rage to be directed?
After a particularly long evening of tending to insufferable patients and maintaining her cheerful facade, she retreated to her lab. And the presence of the prisoner beneath her floors was too much to resist. She was angry. She was upset. There was this ache in her chest that crawled through each of her limbs, an energy yearning to be released, and so she opened the trapdoor to the cellar and dropped down into the shadows with more vigor than could be excused as anything but excitement.
“Good evening,” Shinobu greeted her lab rat, lighting the lamp that sat ready on the table in the corner of the cold, dark room. The creature in the cell across from her cowered at the light and she delighted in the sound of its frightened hiss. “No prying questions, this time, don't worry. I'm done tormenting you for answers you won't give. I’m not going to ask anything of you tonight.”
She turned to stare at it with an eerie smile and the demon just watched her, chest rising and falling in an effort to contain its bloodlust as the scent of her, alive and warm and full of sweet blood, flooded the room. The hunger on its face disgusted her. Demons truly were evil beings. Her smile faded to something blank and unfeeling as she opened the door to the cell.
“Just sit tight,” she muttered, and pierced her sword through the demon's neck.
God, the satisfaction that was granted to her at the sick tearing of flesh was such a relief. Something eased in her chest the instant her blade pierced the demon's throat, the force of the stab she'd delivered driving it back against the wall and pinning it there. Her fighting technique relied on the quick bursts of strength she used to thrust her blade, making the sheer power of the attack she'd just delivered possible- she wasn't anywhere near strong enough to really cut a demon's neck, but piercing it? Easy. And so, so rewarding, so much so that her smile almost returned at the demon's strangled cry of pain.
Shinobu walked closer as the evil creature cowered against the wall and fought against the chains bound to the floor as if to try and remove the weapon. The links of metal were too strong, though, and, bound to the floor, only offered it a few feet or so of slack had she not pinned it with her sword. She'd effectively limited its movement to the point of helplessness, and she made a shushing noise as something desperate and pained gurgled from the demon's throat. If she had any energy left to maintain her happy persona, she might have commented cheerfully that her patients were sleeping and to be quiet so as not to disturb them, please, but at the moment she had no such resolve to do so.
“If you make another noise I'll kill you,” she stated instead, selecting a sharp dagger from a pocket inside her haori and coming to stand in front of the demon with a blank stare. “You can scream in your head.”
Without further ado she raised the blade and, with all her strength, drew it across the demon's body to open its stomach.
The tear of flesh and the strain on her arms as she cut deep into its body was the perfect outlet for all her pain. Relief. That was the first thing she felt as guts poured from the monster's stomach, as though the blood and intestines were the tension in her heart finally spilling, finally free. She immediately drew her blade back to stab it again, in its heart this time, and tore. Blood spurted out and she was glad she'd removed her beloved sister's haori before entering the cell, as the sheer amount of red that splattered over her chest and face was absurd. Not all demons had blood- some anomalies had evolved so far from a human state that the only blood present in their bodies was that that they drank from humans. She was glad this one did. It made it feel more real.
The demon tried to fight her, as she mutilated its body. The thrashing was pathetic, almost as pathetic as the desperate rasping sounds it made. She leaned back to watch its flesh slowly knit back together, with such a painstaking speed that made the extent of its weakness incredibly clear. After days trapped in the cellar with no human flesh to sustain it, the demon had grown frail, unable to heal and attack as usual. And yet it recovered. The damage she'd inflicted would have killed any human for sure, but this horrible creature managed to evade death no matter her efforts. Almost no attack could end them. The unfairness of it all was infuriating. How was it that humans, fragile and mortal beings with souls and minds and loved ones could fight and fight for life just for it to be taken so easily while demons- these man-eating, soulless creatures- could persevere through almost anything?
Something sharp jabbed in Shinobu’s chest as her sister's face came to mind. Kanae had been so good- kind, hardworking, brilliant and empathetic, yet she'd been ripped away from her by something cruel, selfish and evil. Some tried to argue the point that demons didn't have a choice in the matter of their sins, that they had to kill in order to survive and that deep down they were still human. Shinobu knew better. Any being with even an ounce of empathy would end themselves the instant their existence became dependent on taking the lives of others. It was as easy as stepping into the sun. So no, she wouldn't spare demons even a little bit of sympathy. They chose to take lives for their own. They chose to take humans and make of them not people, but meals. They were sick. Disgusting. Inherently evil.
And the rest without the state of mind to consider such principles of morality, who operated solely on bloodlust? They were animals, simple as that. Which is why she felt so comfortable gouging out the contents of her prisoner's torso.
“Stay still, now,” She gritted through clenched teeth, and a broken, strangled noise of anguish made its way from the demon's mouth as she took a fistful of its intestines and pulled. The guts were slick and rubbery in between her fingers, and made a horrid, dull ripping sound when they broke from its body. Shinobu looked down at her handful of tissue wet with blood and examined it, holding it up for her prisoner to see. “These are remarkably similar to digestive systems seen in dogs, you know. More fit to processing meat.” She spoke as if simply analyzing the gore she'd created, as though she was doing this for any scientific reason at all- but really, there was nothing motivating her but rage.
The guts dangled and glimmered in the candlelight, and if she hadn’t devoted her life for years now to studying demons and healing those mutilated by them she likely would've been made sick by the smell. And the texture. She let the intestines drop to the ground. They piled with a sick squelching sound on the cold stone floor, and the demon chained before her trembled at the graphic slop sound of its insides. Fucking animal. She scowled and her stomach churned not with disgust at the gore but pure hate as its chest rose and fell desperately. “I'd set those aside to use as samples but I don't think I have the patience tonight. And anyways, there's more where that came from.”
The demon would just have to hope it had enough energy left to regenerate, otherwise it wouldn't be able to renew its power by digesting flesh- and that was even if it somehow got any. Shinobu kept her test subjects sustained on the smallest amounts of blood, just enough to keep them alive, for as long as she had a use for them. The process of capturing a demon was not an easy one, after all. Killing it would be a waste. ‘Merciful death’, Kagaya-sama insisted. Yeah, right. She loved him but he was not a scientist. No, she would do what she needed to her lab rats- they weren't deserving of mercy, anyways, and she was working towards a good cause.
“Maybe I'll take an eye, though,” she muttered to herself, knife in hand, but before she could a timid voice sounded behind her and she froze.
“Shinobu?” Mitsuri asked, voice unmistakable despite the way it shook, and for the first time that night something uneasy curled in her gut.
The Insect Hashira glanced over her shoulder, lowering her blade as she did so, and looked at the other girl with a warm smile. Mitsuri was standing at the bottom of the steps that led to the cellar, her arms limp at her sides- and there was something on her face that Shinobu hadn't seen directed towards her before. Confusion, yes, but there was something else, something she couldn't put her finger on. She instantly turned away from the demon and pocketed her dagger, greeting the other girl with a smile. “Oh, Mistsuri! I didn't see you there.” She used her first name strategically, softened her gaze with a purpose. “Why are you here?”
The pink-haired woman wasn't really looking back at her, though. Her gaze was fixed instead on the blood drying sticky on the Insect Pillar's face, on the guts pooled on the ground. Shinobu’s lips tightened when her eyes drifted to the sword jammed into the demon's throat. The poor girl looked like she was about to be sick. For a demon slayer, she had quite the weak stomach.
“You seem to have caught me in the middle of a little research! Sorry about that,” The shorter of the two laughed lightheartedly, stepping out of the cell and closing the door with a little more force than necessary. The clang of the metal colliding was the only noise in the space besides the labored breathing of the creature behind her. There was silence for a moment. “I know you're a bit sensitive to these things. I should've shut that door, then I could have warned you.”
Mitsuri's gaze finally met hers. “You were… doing research?” She whispered, and the way her voice wavered made the wariness in Shinobu’s gut expand. “Yes,” she confirmed quietly, clasping her hands behind her back. “Collecting samples, you know. To further develop my poison.”
No one spoke for a moment, and the silence as she maintained her cheerful smile made the emotions swell in her throat all over again. Two seconds. Three, then four, then-
“Shinobu-,”
“How about we have some tea?” She offered brightly, pushing away everything else to make room for the false cheer in her voice. “It's late, but Aoi bought this lovely blend that is so nice around sunset. It's quite relaxing. I'm sure you're tired from your day and I admit I am too, so why don't you head out to the garden and I'll join you after I change?”
The taller woman hesitated, but after a glance at the mess in the cell her face whitened further and she nodded silently before turning to walk up the stairs. Shinobu listened to the sound of her footsteps and only once they faded from her office above did her smile drop.
The silence was suffocating, now, and she stood still for quite a while as she processed why. She hadn't wanted her friend to see her doing that. Or anyone to see, for that matter. The other girl was far too empathetic and kind for her own good, and she knew Mitsuri likely wouldn't approve- she didn't understand. She was naive. But in the end it was just a little misunderstanding, nothing more to it. So why did she feel so… on edge? Uneasy?
Shinobu recalled the expression that had been on the Love Hashira's face when she turned around. Confusion, that was it. But also-
Fear, she realized to herself as she stared thoughtfully at the wall.
For an instant, Mitsuri had feared her.
Shinobu stood in silence for a moment before turning to leave the basement, shutting the trapdoor behind her and leaving all her emotions down within the stone walls, curled up with the demon she'd imprisoned.
She fixed a smile on her face and went to change.