The air in the Captain-Commander's office was perpetually heavy, steeped in centuries of authority and the faint, ever-present scent of smoldering ash. Yamamoto Genryūsai Shigekuni did not look up as Captain Isshin Shiba entered and offered a respectful bow.
"Isshin," Yamamoto's voice was a low rumble, devoid of preamble. "The Third Seat of your division. His retirement is now formal."
Isshin straightened, his usual boisterousness carefully banked in this presence. "It is, sir. He's earned his rest in the Senkai gardens."
"Time has come to test the one you suggested for the seat.," Yamamoto stated. He slid a single, stark dossier across the polished wood of his desk. "This is your candidate's trial. A final test to see if the metal has become worthy of the rank."
Isshin picked up the file. The name on the front made his eyebrows rise slightly, but he said nothing, opening it to read the contents. The further he read, the more his expression sobered.
"Genshiro Kabe," Isshin muttered. "Former Kidō Corps. Barrier Division." While reading he started mumbling to himself, "I remember the incident about him. Though only the whispers. They said he was trying to play god with the soul itself."
"His experiments sought to 'purify' the Zanpakutō bond by stripping it of emotional 'corruption'," Yamamoto clarified, his tone laced with disdain for such hubris. "In his folly, he instead awakened a Zanpakutō that embodies the ultimate corruption entropy. 'Sabitsurugi'. Its command is 'Corrode'."
Isshin whistled lowly, reading the ability description. "Anything it cuts or touches rusts, corrodes, unravels... spiritually. That's not just breaking things, that's un-making them. He can rot Kidō formulas? That's a nightmare."
"Precisely. After his exile, he vanished into the remote districts of West Rukongai. We turned a blind eye, believing his isolation was punishment enough. We were mistaken." Yamamoto's eyes, ancient and fierce, finally lifted to meet Isshin's. "New intelligence confirms he has not abandoned his research. He is now experimenting on lost souls and Hollows, attempting to prove his mad theory that all spiritual power has an inherent death. He is actively causing spiritual collapse, creating pockets of dead space in the Rukongai. This can no longer be tolerated."
He gestured to the dossier. "Your Fifth Seat, Kurozume Akio, has demonstrated the tactical intellect, control, and unique power required for this hunt. Kabe is a scientist, not a frontline brawler, but his Zanpakutō makes him exceptionally dangerous. Conventional force is useless. What is required is precision, adaptability, and a mind that can outthink a heretic. Send Kurozume. If he can capture or eliminate this rogue, he will have proven himself worthy of the Third Seat."
Isshin closed the file, his face set in grim lines. He understood. This was more than a promotion exam. This was the Gotei 13 cleaning up a mess it had allowed to fester, and they were sending their most promising, unconventional weapon to do it.
"Understood, Captain-Commander. I'll brief him immediately."
Akio stood at attention in Isshin's office, his gaze fixed on a point just past the captain's shoulder as Isshin relayed the mission.
"…and that's the situation," Isshin finished, tossing the dossier onto his desk. "Genshiro Kabe. His Zanpakutō, Sabitsurugi, is a real piece of work. It doesn't just cut you; it makes you and your power fall apart. Think of it as accelerated decay. Your Kidō, your Reiatsu, your very Zanpakutō—nothing is safe from its touch."
Akio's mind, a well-oiled tactical processor, was already running. A Barrier Division specialist. A scientist. His environment would be a fortress, layered with traps and Kidō constructs, all of which Sabitsurugi could likely bypass or dismantle. A direct assault was the worst possible approach. He would have to be a ghost, a scalpel, not a hammer.
"His goal is to prove all spiritual energy has entropy," Akio mused aloud, his voice low and analytical. "His experiments will have a focal point, a 'laboratory'. He can't be hiding randomly; he should have chosen a location with specific spiritual properties, likely an area with naturally weak boundaries or a history of spiritual phenomena he can exploit. The file says West Rukongai, District 73. The 'Bleeding Crags'. The geological surveys from the Academy archives note persistent, low-level spiritual interference there. It fits."
Isshin blinked, impressed despite the gravity of the situation. "You've done your homework on the Rukongai."
"It was my home," Akio said simply, the statement carrying the weight of a thousand survival lessons. "Knowing the terrain is the first rule of staying alive. The second is knowing your enemy. He views emotion as a corruption to be purified. That is a critical weakness. His entire worldview is a rejection of chaos, of the unpredictable. He will have a plan for every variable he can conceive of."
A faint, cold smile touched Akio's lips. "But he won't have conceived of me."
Isshin felt a chill that had nothing to do with the room's temperature. In that moment, Akio didn't look like a loyal soldier receiving orders. He looked like a predator being pointed toward prey.
"The Old Man was clear," Isshin said, pushing the dossier toward him. "Success in this mission means the Third Seat is yours. Failure… well, with this guy, failure probably means you end up as a pile of spiritual rust. So don't fail."
Akio picked up the file. "Understood, Captain." He turned to leave.
"Akio," Isshin's voice stopped him. "This isn't a Hollow. This is a former brother-in-arms, however far he's fallen. Remember that."
Akio paused at the door, not looking back. "He stopped being a brother-in-arms the moment he started experimenting on the souls he was sworn to protect. The only thing that remains is the target."
He left, closing the door softly behind him. Isshin stared at the space where he had stood, a complex mix of pride and foreboding settling in his gut. He was sending a shadow to hunt a rusted ghost. He could only hope the shadow was darker.
Back in his own quarters, Akio spread the contents of the dossier on his desk. Maps of District 73, old schematics of Kidō Corps barrier protocols, everything they had on Sabitsurugi's observed abilities. He cross-referenced it all with his own knowledge, his fingers tracing the potential routes through the crags.
Sabitsurugi. Corrosion. Entropy. A power that unraveled the very fabric of spiritual constructs. It was the antithesis of creation, of order, of life itself. It was a dangerous, insidious ability.
But every power had its limits. Corrosion took time. It was a process, not an instantaneous event. The key would be to never let the blade make solid contact. Speed, misdirection, and absolute precision would be his weapons. His Shadow Network could sense disturbances, the spiritual "rot" left in Kabe's wake. His Position Play would allow him to strike from angles Kabe couldn't possibly defend against simultaneously.
He looked at the artist's rendering of Genshiro Kabe—a man with tired, fanatical eyes and a stern mouth. A man who saw the world as a flawed equation to be solved.
"All things rot," Akio whispered, echoing the rogue's final words to the Kidō Corps. "But shadows don't rust."
He closed the file. The hunt was on.