While Kazuma was managing Kaien's crisis in the Seireitei, a supposedly routine incident unfolded in the World of the Living.
Led by Shūhei Hisagi as the senior sixth-year instructor, Momo Hinamori, Izuru Kira, Renji Abarai, and several other first-year students deployed to the human world to participate in a simulated Hollow extermination exercise.
Organized into standard three-man cells, Momo's trio naturally formed a single combat team.
Following Shūhei's strict instructions, the recruits stepped through the Senkaimon and arrived in the World of the Living.
Surveying the rusted metal and broken concrete of their designated zone, Renji crossed his arms.
"This place looks like an abandoned factory."
Kira slapped the back of the red-haired boy's head and rolled his eyes.
"That's obvious. The Academy has to drop us in a deserted area. Otherwise, civilian casualties would spike if someone misfired a Kidō."
"Idiot, I was just making an observation," Renji grumbled, rubbing his stinging scalp. "Why did you have to hit me?"
Stepping between the two boys, Momo raised her hands to mediate and sighed.
"Both of you, stop arguing and focus. Let's find the simulated targets so we can complete the mission and go home."
Serving as the necessary peacekeeper, Momo knew this three-person team would have fallen apart weeks ago without her constant intervention.
Curling his lip, Kira drew his Asauchi and muttered that since Momo had spoken up, it was time to start moving.
While the three recruits bickered in the dirt, a massive, invisible Hollow materialized atop the rusted factory roof, quietly observing the trainees below without triggering a single spiritual alarm.
As time ticked by, several teams completed their extermination tasks and returned to the primary assembly point.
Renji's trio, however, was still searching the perimeter when Renji finally spotted a target.
Engaging the simulated Hollow with a heavy swing of his Asauchi, he quickly retreated to create distance.
"I found one! Hurry over!"
Arriving just in time to capitalize on the opening, Momo raised her palm and chanted the brief incantation.
"Hado, #31 : Shakkahō!"
A sphere of red flame struck the simulated Hollow, but as the smoke cleared, it became apparent that the blast had not caused lethal damage.
Seizing the opportunity, Kira blurred forward and cleaved the staggered target in half with a clean downward strike of his blade, finishing the simulation.
"Impressive, right?" Kira boasted, resting his sword on his shoulder. "I took it down with a single strike."
Renji scoffed, dismissing the claim.
"Give me a break. If Momo hadn't blasted it first, there's no way you could have finished it in one hit."
Stepping between them once again, Momo pushed their shoulders apart.
"Can't you two stop fighting for five minutes? The mission is done, so let's head back to the assembly point before Shūhei yells at us."
As the three playfully shoved one another toward the rally point, Momo suddenly paused, a cold chill running down her spine.
Turning to look at the empty rooftops, she saw nothing but rusted metal, yet she could not shake the heavy, suffocating feeling of unease settling over her.
Noting that the designated time limit had expired, Shūhei activated his communicator and ordered the perimeter lockdown.
"Barrier squad, respond. Prepare for withdrawal."
After calling twice and receiving only dead static in return, Shūhei's grip on his sword tightened.
Something had gone wrong.
A block away, the members of the Barrier squad already lay dead, torn apart by the invisible giant Hollow.
As Shūhei tried adjusting his radio frequency, a female sixth-year student beside him suddenly screamed his name.
Turning his head, Shūhei's eyes widened in horror as a massive, towering Hollow dropped from the sky.
How is this possible? Shūhei thought, his blood running cold. A Hollow this large bypassed the perimeter without anyone noticing?
With a brutal swipe of its jagged claw, the Hollow crushed the female student on the spot.
"Kanzawa!" another senior student screamed, drawing his blade and charging the beast in blind rage over his companion's death.
"Aoshika, don't break formation!" Shūhei roared, reaching out to stop him.
Unsurprisingly, the charging senior was swatted aside and killed by the massive Hollow before his blade could even connect.
Frantically thumbing his communicator to broadcast a distress signal to Soul Society, Shūhei drew his blade to block the Hollow's descending claw and roared at the terrified first-years.
"Run! Scatter and hide!"
Panic erupted as the trainees fled for their lives.
Though Shūhei did his best to parry the beast's relentless strikes, the Hollow's immense strength battered his guard, allowing a sharp claw to graze the right side of his face.
Blood streamed down his cheek, staining his eye and blurring his vision.
The Hollow raised its arm to deliver a fatal, crushing blow to the wounded instructor.
Just as Shūhei braced for death, three unreleased Asauchi crossed in front of him, intercepting the massive claw with a shower of sparks.
Struggling to lift his head, Shūhei found Momo, Renji, and Kira standing over him, their boots digging into the concrete as they strained against the Hollow's weight.
"Why didn't you three run?" Shūhei choked out, holding his bleeding eye.
"Sorry, Senpai," Renji grunted, his arms trembling under the strain. "We couldn't just leave you here to die. Please forgive us for disobeying orders."
When the giant Hollow first appeared, the trio had been paralyzed by fear.
But seeing their instructor about to be slaughtered gave them the desperate courage to step forward and block the strike together.
"Senpai, let's get out of here!" Kira yelled, helping Shūhei to his feet as the group broke formation and began to run.
However, the Hollow pursued them relentlessly, its massive strides easily closing the distance.
"Running isn't going to work," Renji shouted, skidding to a halt and turning to face the beast.
Following his lead, Momo and Kira stopped, raising their hands in unison as they chanted together.
"Hado, #31: Shakkahō!"
Three overlapping blasts of red flame struck the Hollow square in the chest, temporarily blinding it and hindering its movement.
"Go!" Shūhei yelled, grabbing their collars and pulling them along as they resumed fleeing down the alley.
As they ran, the space in front of them suddenly distorted, tearing open to reveal several more massive Hollows blocking their only escape route.
"It's over," Shūhei muttered, his sword arm dropping as the group halted, trapped between the monsters.
In this situation, fighting was pointless.
Just as the students braced for the end, a blinding flash of silver light surged through the alley, cleanly bisecting the closest Hollow before it could strike.
"Sorry we arrived late," Aizen's smooth, gentle voice echoed through the alley as he stepped out of a Senkaimon alongside Gin Ichimaru.
"Leave the rest to us. You can rest now."
Drawing his short sword with a wide, fox-like grin, Gin pointed the blade at the remaining monsters.
"Shoot to kill, Shinsō."
The blade extended like a spear of light, sweeping across the alleyway.
Wherever the steel touched, the giant Hollows were shredded and dissolved into ash.
Gin's movements were as graceful as a dance, each strike precisely hitting its target without a single wasted motion.
Sensing the overwhelming Spiritual Pressure radiating from the Captains, the final giant Hollow turned to flee, but its speed was useless.
Aizen materialized directly beside the beast with a blur of Shunpo, lightly waving his hand to unleash a crushing wave of Reiatsu that instantly reduced the monster to dust.
Sheathing his sword, Aizen turned to the terrified students and offered a warm, reassuring smile, as if the massacre had been nothing more than a minor disturbance.
"Alright, let's return to the Seireitei. This incident has frightened you enough for one day."
At that moment, Aizen's gentle, heroic figure was deeply etched into Momo Hinamori's heart.
Watching the tall Captain stand amid the fading Hollow ash, she felt an overwhelming surge of gratitude and admiration.
If she knew that the entire massacre had been a calculated test orchestrated by Aizen to manipulate their loyalty, she would have cursed his name.
But unaware of the truth, the young girl simply believed Aizen was a great Captain and a savior worth following to the ends of the earth.
Similarly, Shūhei, Renji, and Kira felt profound respect for the man.
The surviving students silently vowed that after graduation, they would do whatever it took to join the Fifth Division, driven by deep gratitude toward the man who had saved their lives.