Chapter Text
Shinazugawa Sanemi was not a paranoid man. He was a realistic man. A vigilant man. A man who paid attention to his surroundings because failing to do so got people killed.
Which was precisely why the absolute, baffling nonsense occurring between Shinobu and Tomioka was driving him out of his mind.
It had started small—so small that Sanemi had initially written it off as a fluke. Five months ago, after a particularly grueling Hashira meeting, the Corps had been assigned new patrol shifts. Naturally, most of them dispersed immediately. Iguro left for his mission far away, Uzui made some loud, obnoxious exit about being flashy, and Gyomei began his usual silent walk back to his quarters.
Sanemi had stayed behind briefly to double-check a report with the Master. When he stepped out onto the porch, he expected the courtyard to be empty. It wasn't.
Tomioka was sitting on the wooden engawa, staring blankly at the garden pond. And sitting right beside him—close enough that her haori brushed against his—was Shinobu. She was sipping tea from a ceramic cup, chatting effortlessly about some new strain of poison she was cultivating. Tomioka wasn't saying a word. He just sat there, looking like a doll, listening.
Sanemi had snorted, muttering under his breath about Tomioka’s pathetic inability to take a hint, assuming Shinobu was simply cornering the idiot to torment him. Shinobu, after all, had a razor-sharp tongue and a habit of prodding people until they snapped. It made sense that she’d pick on the one guy who lacked the verbal capacity to fight back.
Except, as the weeks went on, Sanemi realized something terrifying: Tomioka wasn't being cornered.
They were paired together on missions more than any other Hashira. That part made tactical sense—Tomioka was a powerhouse of defense with his Water Breathing, while Shinobu possessed the speed and medical lethality to finish off fast, venom-susceptible demons. They complemented each other on the battlefield. Sanemi understood this.
What he didn't understand was what happened after the battle was over.
A month ago, Sanemi had been returning from a bloody clash from the south. He’d dropped by a small Wisteria Family Crest house to patch up a split shoulder before heading to the Butterfly Mansion. As he entered the courtyard, he spotted them.
Shinobu was sitting on the engawa outside her room, meticulously wrapping a clean bandage around Tomioka’s forearm. Her movements were professional, and precise. But what caught Sanemi’s eye was the quietness of it all. Shinobu was usually a force of cheerful, performative energy—always smiling, always dropping polite, biting remarks. Yet here, she wasn't putting on a show. Her shoulders were dropped, her posture relaxed, and her quiet commentary about proper wound hygiene lacked her usual sarcasm. And Tomioka? The bastard wasn't staring at the wall with his usual expression of arrogant detachment. He was looking right at her hands, responding in quiet, low grunts that Shinobu seemed to understand without needing a translation.
Sanemi had stood in the shadow of the doorway, his eyes narrowed, his blood pressure taking its usual upward spike.
Why him? Sanemi had thought. Out of everyone in the Corps, why is she spending her spare time with the guy who acts like he’s too good to breathe the same air as the rest of us?
Kanae’s memory hovered over Shinobu like a phantom shroud. Sanemi had loved Kanae—her warmth, her kindness, her soft-spoken strength, her relentless hope. When she died, something in Shinobu had snapped, replaced by that rigid, terrifyingly sweet mask she wore every hour of the day. Sanemi felt a sharp sense of responsibility toward her. He couldn't replace her sister, and he certainly wouldn't dare try to play big brother out loud, but he watched over her. He made sure she wasn't pushed too far. He made sure she was safe.
So seeing her choose to spend her precious, rare moments of rest with Tomioka Giyu felt like a personal insult to common sense.
Aside from Mitsuri, whom Shinobu treated with genuine sisterly affection, and her own sisters, Shinobu didn't let anyone get close. She kept everyone at an arm's length behind a wall of politeness. Yet, somehow, Tomioka had slipped right past the barrier without even trying.
Sanemi watched them at the courtyard. He watched them at the gates. He saw the way Shinobu would lightly nudge Tomioka’s elbow to get him to walk in the right direction when he drifted into a daze. He saw how Tomioka, despite claiming he didn't need friends, would quietly stand a pace behind her whenever lower-ranked corps members gathered while she spoke.
It didn't make any damn sense. They didn't make any damn sense.
Standing on the roof of the estate three days before the next Hashira meeting, Sanemi watched the two of them walk down the stone path toward the Butterfly Mansion. Shinobu was talking, gesturing lightly with her hands, and Tomioka was walking beside her, his head tilted slightly toward her to hear her over the wind.
Sanemi’s jaw clenched. The suspicion in his chest had grown from a light annoyance into a full-blown, festering itch. It was sickening. Tomioka was a brick wall with a sword. Shinobu was... well, she was Kanae’s little sister, which meant Sanemi felt a deeply irritating, unasked-for responsibility to make sure she wasn't losing her mind.
Something was going on between those two. Whether they realized it or not, the air around them had changed, and Sanemi was not going to sit back and let Kanae's sister fall for a socially stunted wall without getting some answers first.
With a frown on his face, he turned toward the main grounds. He needed to get to the bottom of this.