Chapter Text
Several months had passed since the defeat of Yhwach.
The scars of war still existed, but they no longer dominated every corner of the Seireitei. Rebuilt walls stood where entire districts had once been reduced to rubble, construction crews had finally begun disappearing from the streets, and the constant tension that had lingered over Soul Society since the Thousand-Year Blood War had gradually given way to something far less dramatic.
The Gotei Thirteen had returned to its familiar rhythm. Patrols resumed. Reports were filed. Disputes were settled. Life moved forward.
For most people, that was a welcome change. For Captain Tōshirō Hitsugaya, it mostly meant paperwork.
Stacks of reports occupied nearly every available space on his desk. Mission summaries, reconstruction assessments, personnel evaluations, budget requests, and incident records formed small mountains around him, each one waiting for a signature, review, or decision.
Hitsugaya set down his brush and leaned back slightly. His eyes moved from one pile to the next. Neither looked any smaller than they had an hour ago.
Suspicious, very suspicious. He was beginning to suspect that paperwork reproduced when left unattended.
The door to his office slid open.
"Captain?"
Rangiku Matsumoto stepped inside with a folder tucked beneath one arm. She looked around the room, then toward the paperwork, then back at him.
For once, she actually looked sympathetic.
"Still alive?"
Hitsugaya didn't even bother looking up. "Barely," he grumbled.
"That's good to hear."
"It wasn't a serious answer."
"I know."
A smile tugged at the corner of her lips. Hitsugaya sighed. "What is it?"
"The Captain Commander wants to see you."
That immediately earned his attention. The brush stopped moving. "The Captain Commander?"
Rangiku nodded. "Immediately."
"Did he say why?"
"No." She tilted her head thoughtfully. "Although if I had to guess, it probably isn't good news."
"When has it ever been good news?"
"Fair point."
The grin that followed suggested she was enjoying this far more than she should. Hitsugaya already disliked where this was going.
The meeting chamber inside First Division headquarters felt unusually empty. Moonlight filtered through paper windows and spread pale reflections across polished floorboards. The room, normally used for larger gatherings, contained only two occupants. That alone was enough to make Hitsugaya suspicious.
Shunsui sat comfortably at the head of the table with a cup of tea resting beside him. Across from him stood Mayuri Kurotsuchi.
The combination was concerning. Whenever Shunsui looked relaxed and Mayuri looked pleased with himself, someone else's workload usually increased dramatically. Hitsugaya had a strong suspicion whose workload that would be.
"Ah, Hitsugaya-kun." Shunsui greeted him warmly. "Thank you for coming."
"I wasn't given much choice."
"No, you weren't."
At least he admitted it.
A low chuckle escaped Mayuri. Hitsugaya ignored him on principle. Several thick folders rested on the table between them.
The moment Hitsugaya approached, Mayuri pushed one across the polished wood. Papers shifted and slid apart as the folder came to a stop. Hitsugaya opened it.
His eyes moved across pages filled with measurements, observations, sketches, and handwritten notes. Several reports had clearly been amended multiple times. Entire sections had been crossed out and replaced with new conclusions, only for those conclusions to be challenged again several pages later.
The deeper he read, the deeper the crease between his brows became. The data itself made sense. The conclusions did not.
One report suggested a spiritual phenomenon. The next rejected that idea. Another attempted to compare it to known Quincy activity.
Several pages later, that theory had been dismissed entirely. The collection felt less like a completed investigation and more like a record of failed attempts to understand something that refused to cooperate.
"What exactly am I looking at?"
Mayuri folded his arms. "A question I would very much like answered myself."
Hitsugaya looked up. "You don't know?"
A twitch appeared near Mayuri's eye. "No."
Hitsugaya blinked. "The scientist who dissects spiritual phenomena for entertainment?"
"The very same."
"And you don't know?"
"No."
Shunsui lowered his cup and hid part of his smile behind one sleeve. That only seemed to annoy Mayuri further.
"The source originates somewhere in the Human World." Mayuri tapped one of the reports. "We have monitored it for months. Every attempt to classify the energy has failed." He slid another document forward. "It is not reiatsu, not reishi, not Hollow-related, not Quincy."
Hitsugaya's gaze narrowed. "Then what is it?"
For perhaps the first time in recorded history, Mayuri spread his hands in genuine frustration. "I have no answer." That worried Hitsugaya more than he cared to admit.
Mayuri was arrogant, insufferable, and occasionally terrifying. But ignorance was not a trait commonly associated with him. If even Mayuri could not identify the phenomenon, then Soul Society was dealing with something entirely outside its experience.
"The fluctuations have been increasing." Shunsui finally set down his tea. Though his voice remained calm, the easy smile had faded slightly. "We don't know whether it's dangerous. We only know it shouldn't exist."
Hitsugaya folded his arms. He already knew where this conversation was heading.
"No."
Shunsui blinked. "I haven't asked anything."
"You were about to."
A grin immediately returned. "You're getting better at this," Shunshui said.
"I'm not going."
"Yes, you are."
Mayuri laughed outright. Hitsugaya closed his eyes.
Of course.
"We need someone reliable to investigate." Shunsui rested his chin on one hand. "Someone capable of making decisions without creating unnecessary complications."
Hitsugaya stared. "Just say my name next time."
"I thought I did."
"You spent thirty seconds describing me first."
"It sounded more professional."
Despite himself, the corner of Hitsugaya's mouth twitched. Only slightly. "What exactly is the assignment?"
"Investigate the source."
"Anything else?"
"Observe and report."
"That's it?"
"For now."
Those two words carried far more uncertainty than Hitsugaya liked. Whenever a mission began with for now, it inevitably became more complicated later.
--
Several hours later, he stepped through a Senkaimon.
Cool night air brushed against his face as he emerged atop a tall building overlooking the city. Thousands of lights stretched toward the horizon.
Vehicles flowed through illuminated streets below like streams of moving color. Restaurants remained crowded despite the late hour, conversations drifted upward from sidewalks, and people carried on with their lives completely unaware that another world existed alongside their own.
Hitsugaya stood quietly for a moment. The Human World felt familiar, almost comforting.
Immediately, he felt it—not a presence or reiatsu, but a subtle distortion woven into reality itself. It was faint, but unmistakable. Whatever Soul Society had detected, it was real.
--
A day became several before he even realized it.
The investigation had turned far more complicated than expected. Every clue seemed incomplete, and every answer only led to more questions.
Still, one pattern refused to disappear. Again and again, the strongest readings pointed toward the same organization.
SHIELD. A human agency with enough resources and secrecy to make even Soul Society appear surprisingly transparent.
The more Hitsugaya observed them, the more convinced he became that they were connected to the anomaly. Whether intentionally or otherwise remained unclear.
A week later, he stood atop a rocky ridge overlooking one of their facilities. Floodlights illuminated fences, security checkpoints, and patrol routes below. Armed personnel moved through the compound while vehicles entered and exited at regular intervals. Nothing about the facility appeared unusual, yet the disturbance always led back here.
A Hell Butterfly appeared beside him. Its wings shimmered softly against the darkness.
"Report." Shunsui's voice emerged from it.
Hitsugaya kept his eyes fixed on the compound. "I found the source."
"Confident?"
"Yes."
"What is it?"
Hitsugaya watched a transport vehicle disappear behind one of the buildings. "I still don't know."
A sigh echoed through the butterfly. "That answer is becoming annoyingly common."
"It would help if I had better information."
"It would help if we had better information."
Hitsugaya couldn't argue with that.
Shunsui finally asked. "Do you need support?"
"No."
"Good," the amusement returned to Shunsui's voice. "I wasn't planning to send any."
Hitsugaya stared at the butterfly. The butterfly offered no explanation. "Captain Commander."
"Yes?"
"That wasn't funny."
"I disagree."
The communication ended.
Hitsugaya shook his head before turning his attention back toward the facility.
Something had changed. The disturbance felt stronger than before. Not because he had grown accustomed to it, but because it was growing. The vibration beneath reality had become impossible to ignore. Whatever process was occurring inside the facility was approaching a critical stage.
Then alarms erupted. Red warning lights flashed across multiple structures. Personnel began moving with obvious urgency. Security teams rushed into position. Even from a distance, Hitsugaya could tell something had gone wrong.
A surge of energy exploded from deep within the facility.
His eyes widened. The sensation struck him like a wave. It was unlike anything he had ever encountered. Every instinct he possessed told him he was witnessing something entirely foreign to the natural order he understood.
The pressure continued to rise. It was unstable and violent, growing stronger with every passing second.
He stepped forward. Then another. Observation was no longer enough.. His body vanished in a flash of shunpo as he raced toward the facility.
Far below, hidden beneath layers of steel and concrete, the Tesseract was beginning to awaken, and neither Soul Society nor SHIELD had any idea how much trouble was about to walk through that portal.