Disappearances in Soul Society

 is an event that occurs over 100 years before the battle in the Fake Karakura Town against Sōsuke Aizen and his forces. It is an incident that begins series of events that leads to the creation and exile of the Visored as well as the exile of Kisuke Urahara, Tessai Tsukabishi, and Yoruichi Shihōin.

Prelude
Nine years after Kisuke Urahara was promoted to captain of the Twelfth Division, there are three souls in the Rukongai who find themselves suffering from an unknown process. They contort in agony and spew a mysteriously white substance from their mouth. As they hold onto their necks, they choke all the while.

The pressure on their bodies becomes too much and they explode, completely turned into the white substance which lands on a nearby umbrella that is shielding three observers. One of them concludes that an ordinary soul cannot be kept a prototype in their experiment as their body breaks down too easily. His comrade asks if they should quit due to this, but the first person insists they will continue with their actions.

In the Seireitei, Captain Shinji Hirako is out walking with his Lieutenant Sōsuke Aizen when he spots Captain Urahara with his Lieutenant Hiyori Sarugaki and 3rd Seat Mayuri Kurotsuchi coming from the opposite direction. Hirako cheerfully delivers a greeting which Urahara returns with equal enthusiasm. However, Hirako is soon bemused by Urahara's refusal to use his first name and choosing to speak so formally to him. He then greets Kurotsuchi cheerfully by using his first name. The officer takes offense to this and insists he address him formally rather than informally. Even more perplexed, Hirako takes back his words, asserting he's the pain rather than Urahara.

Changing the subject, Hirako asks them if they have heard the latest news that is spreading around the Seireitei. Urahara asks what he is referring to, but Hirako is interrupted by Hiyori before he can answer. The small lieutenant delivers a hard kick to Hirako's lower back, causing the captain to fall to the ground in pain. Stunned, he demands to know why she attacked him so ferociously. Hiyori angrily wonders why Hirako did not greet her, asserting that she is still waiting for a greeting that had been only given to her fellow comrades.

Hirako inquires as to why he should greet her at all, prompting Hiyori to insist that he always leaves her out despite it being customary to greet someone when meeting them on the street. Hirako strongly disagrees with this assertions, maintaining that he can greet whoever he wants without requiring her approval since he is a captain while Hiyori is not. The rest of his words are cut off as Hiyori begins to hit him and Hirako is forced to defend himself. The two begin to scuffle on the ground while Urahara smiles awkwardly at the situation.

As the two of them continue to wrestle on the ground, Aizen turns to Urahara and continues the conversation Hirako had begun before Hiyori's angry interruption. He asks the captain if he has had any news of the gossip, but Urahara shows he has not as he asks Aizen what the news is. Aizen informs him that there have been mysterious deaths occurring in the Rukongai. Behind him, Shinji angrily declares that he wanted to tell Urahara while having to hold Hiyori down and sardonically thanks his subordinate for ruining his fun on the matter.

Curious and stunned, Urahara asks what they mean by strange deaths. Hirako elaborates that residents in the Rukongai have been vanishing for the last month and nobody can tell why. Confused, Urahara asks if they have simply run off. In response, Hirako insults him and asserts that he didn't say that they disappeared by going missing. Hirako maintains that he means that they have actually been disappearing as they leaves behind their clothes with no other evidence. Instead of their clothes also turning into spirit particles upon their deaths, they think their human form is somehow being annihilated while still alive and causes them to vanish.

This serious news greatly puzzles Urahara, who wonders how a soul can completely lose control in maintaining their human form before dying. Turning away from him, Hirako apologizes for confusing him about the situation. He elaborates that he was repeating the theory from Retsu Unohana. He is also quite adamant that, even though he's just explained it to Urahara, he really doesn't understand the possibilities either. He states that it has been decided that more evidence needs to be gathered and that the task has been assigned to the Ninth Division.

The 9th Division Investigates
At the same time, a team of Shinigami from the Ninth Division have been dispatched into the Rukongai to investigate the area in which the disappearances have been occurring. Their job is to find more evidence so that the reasons for these vanishings can properly be concluded as the current theories have no supporting evidence other than the clothes that are being left behind by those who are disappearing. The high ranking members of the Ninth Division march through the Rukongai. The team includes Captain Kensei Muguruma, Lieutenant Mashiro Kuna, 3rd Seat Heizō Kasaki, 4th Seat Shinobu Eishima, 5th Seat Kaname Tōsen, and 6th Seat Izaemon Tōdō.

From the rear of the group, Mashiro demands to know what exactly Kensei means when he says that he doesn't know what they are dealing with in this investigation. Agitated, Kensei tells her to quit whining and asserts that when he says he doesn't know what they are dealing with, he means just that. Mashiro insists that they should wait at the barracks for their report since a ten-man team of Shinigami had been sent out in advance. Getting more angry, Kensei asserts that the lack of any report is the reason they are venturing out to investigate themselves.

Mashiro continues to insist that this isn't the job for a captain, claiming that Kensei is just bored, impatient, and wants to go out when they should have waited for reports. Her voice takes on a whining note to it. Kensei's impatience with his lieutenant's antics heightens until the tension in him snaps. He angrily turns to attack Mashiro, but is grabbed and held back by several of his subordinates as Eishima reminds him that that Mashiro is always trying to get a reaction of out of him with her antics.

Trying to calm himself a little, Kensei shrugs off his officers and informs Mashiro that he does not recall even asking her to come along on the mission anyway. He tells her that she shouldn't have come and advises her to return to their barracks and get some sleep or do whatever she wants to do. Mashiro pouts at this suggestion, calling Kensei a dummy for not remembering that lieutenants must follow their captains during missions. She insults his intelligence several times before his temper snaps again. By that time Mashiro has entered a tantrum, rolling around on the ground and crying about how hungry she is. Eishima asks Kensei on what they should do with Mashiro. With a look of irritation, Kensei simply remarks to leave her.

Suddenly, a ominous wail catches the attention of the Shinigami. They spot several young souls fleeing from a very large Hollow with a long neck. Initially they are stunned by the size of the creature, with Kasaki commenting on the sheer size of the monster. Undisturbed, Kensei withdraws his Zanpakutō and orders his subordinates to attack the Hollow and save the children. His officers obediently comply without any hesitation. All four of them draw their own blades and attack the Hollow as one.

One of the young souls is flung away by the persistent Hollow when it screams out from the attack. The child, Shūhei Hisagi, looks up and notices the approach of the dominating presence of Kensei standing over him. The captain moves to the offensive, releasing his Zanpakutō's Shikai, Tachikaze. He uses its special ability to defeat the Hollow by cutting it apart at various points of its large body. The Hollow falls to the ground as Kensei calmly looks on at the chaos.

The captain looks around as his subordinates assemble about him and asks if everybody is alright. When they confirm that they are, he notices Hisagi kneeling on the ground. As the child sobs, he loudly demands to know why Hisagi is doing so. He maintains that the child should be happy and smile since he survived the attack. Kensei then produces a rather forced smile of his own for the child to prove as an example, but the result is quite terrifying. With a befuddled expression at his captain's actions, Eishima informs Kensei that his attempt to cheer the child is not helping as he is scaring him.

Kensei rejects this theory while he pulls the young soul to his feet and asks him his name. He becomes more demanding when the boy hesitates. Hisagi manages to stutter several times before providing his name nervously. Kensei tells Hisagi that his name is a strong one and orders him to stop crying. However, Hisagi continues to sob and cry from still being frightened, much to Kensei's displeasure as he continues to try and dissuade him from doing so. He sighs after a while and asserts that the situation is quite a pain.

Just then, Mashiro comes upon the scene calling out her captain's name to try and get his attention. When Kensei sees her, he demands to know where she was during the fight. Unashamed, she replies that she was in the bushes behind her before revealing that she found something of importance. Mashiro then holds up a shihakushō and insists that the bushes are filled with them as she has found ten complete outfits. Upon learning about her discovery, Kensei's expression becomes one of shock and sheer horror.

Kensei begins to evaluate the situation, weighing the evidence that Mashiro has brought them. He murmurs out loud about there specifically being ten pairs of shihakushō that were discovered. Clearly disconcerted and worried, Eishima states aloud that he understands where Kensei's train of thought is leading. However, Mashiro is at a loss as to why Kensei and Eishima are so focused on the fact that there are ten pairs of uniforms. Shaking with tension, Kensei reminds her that ten is the exact number of Shinigami that were sent ahead of them.

Unconvinced that this means the team are also victims of the same vanishings, Mashiro wonders aloud if they could have just simply removed their own clothes. Kensei disproves this theory by inquiring how they would be able to remove their shihakushō without untying their Obi and how they would be able to remove their socks without first taking off their sandals. Because these objects are all still in place, they fits with the original style of disappearances where the victims are simply losing their human form and leaving behind their empty outfits as they were before they vanished.

Kensei gathers himself and begins to deliver orders to his subordinates. He first orders Eishima to report to Central Command that the disappearances have claimed their first Shinigami victims; Tōdō is ordered to get researchers from the Twelfth Division due to the possibility that an unknown pathogen is the cause for the breakdown in the soul; Kasaki is ordered to contact a patrol squad in order to obtain a tent so that they can set up camp in the area that night. Kensei determines that the culprit could make their way to the Seireitei so he intends to crush them there and then before they can reach their target. His officers acknowledge his orders and rush off to carry them out.

With his fellow Shinigami heading off to their intended destinations, Tōsen asks his captain what he should do in the meantime. Kensei orders him to follow his lead as they are going to start checking out the general area. He then turns to the youngsters, who are still hanging around and tells them that they should get away from the area and go home as it is dangerous. As Kensei looks away, his undershirt is pulled back slightly to reveal the 69 tattoo on his chest. The captain makes quite an impression on Hisagi as the young boy stares at the tattoo for a long time.

Call Forth the S.R.D.I.
At the Shinigami Research and Development Institute, Kurotsuchi is examining a test-tube filled with a mysterious liquid. He notes to himself that the tube feels right. He then turns behind him and begins to yell at Hiyori to hurry along as he needs the containers she is carrying for him. Impatient at Hiyori's pace, he tells her that the day will be over by the time she arrives. Hiyori then smashes the containers on the ground in a rage and begins to insult him for being nasty when she was being nice and helping him out.

Unaffected by Hiyori's fit, Kurotsuchi asks her why she is suddenly so angry as he really doesn't see an issue to be annoyed over. Hiyori declares heatedly that he is too fussy and wonders why she should be made to help him in any way since she is a lieutenant. She goes on by asking him what seat he is. Kurotsuchi rolls his eyes at this, and tries to avoid answering the question by asserting that things as trivial as ranking systems do not concern him. Hiyori calls his bluff and reminds him that he is a 3rd Seat Officer, and thus cannot order her around. However, he makes a simple retort by reminding her that he outranks her while in the in S.R.D.I. so she should obey him.

Angry over Kurotsuchi's statement, Hiyori screams out for her captain with bloodshot eyes full of agitation. Urahara appears, carrying an object over his shoulder. He tells them to quiet down a bit, insisting he didn't much sleep. Hiyori begins to demand he reprimand Kurotsuchi, but she cuts herself off upon seeing the object that Urahara is carrying. She asks what it is, to which Urahara tells it is a prototype Gigai. Urahara informs her that he thinks he may be able to help those losing their human form by placing their soul in a human-shaped object before they dissipate, revolutionizing Gigai technology in the process.

Their conversation is then interrupted by the arrival of Tōdō on Kensei's orders and he asks if Urahara is present, explaining who has sent him. Urahara invites the Shinigami inside and Tōdō explains the predicament to Urahara regarding the missing Shinigami victims. Urahara insists that he understands the dire need in the situation and will make his selections for investigators and send them out to the site right away. He then advises Tōdō to report back to his captain in the meantime and the officer agrees.

When the officer leaves, Urahara informs Hiyori that he has chosen her to carry out the assignment. His lieutenant is livid, believing one of the lower Shinigami should carry it as she points at Akon. This causes Akon to mention that all she does is complain, so she should just retire her position if she cannot handle it. Hiyori is enraged and tries to kick him, which Akon dodges. Hiyori's frustration then increases when Akon reports he is finished with his work and Kurotsuchi compliments him. Urahara apologizes to Hiyori, stating that she is the only subordinate he trusts to carry out such an important task. He notes that he doesn't mind if she wants to bring others, but it is critical that a sample from the site is taken and he can rely on her. Convinced by these words She reluctantly agrees to the task, insisting it will cost him big later on.

Fall of the 9th Division
Tōdō returns to the investigation site where Eishima and Tōsen are standing guard outside the tent Kensei has set up. Tōsen tells Tōdō that he is late, but the Shinigami tells him to give him a break as he had a longer distance to travel. He then tells Tōsen to go rest and he will take over watch. Tōsen disagrees, saying they all should keep watch. Eishima states that they are all going to take turns in rotation and that Kasaki and Kensei are currently resting inside the tent before it’s their turn.

Inside the tent, Kensei is staring pensively at the food stewing in the pot in front of him. He glances over at his sleeping lieutenant and marvels at how Mashiro can sleep so soundly during a time of such danger. Noticing the top of her uniform falling open, he reaches over and tries to fix her top so that her breasts don't fall out. However, she grabs his hand in her sleep and tells him he is a bad boy, which annoys her captain. He verbally insists she should stop talking to him like that or he will beat her up.

A sudden scream from outside the tent alerts Kasaki and Kensei that there is a problem. They rush out to find the other officers felled with Tōdō glancing at them. Kensei's initial impression is that Tōdō has betrayed them, before seeing Tōdō also collapse bleeding to the ground. Ordering Kasaki to look for the attacker, Kensei tries to wake Mashiro. However, Kasaki is cut down before he is able to wake her. Suddenly the world around Kensei goes dark. He is stunned to find himself stabbed from behind through his chest. Deeply injured, he manages to turn his head to look at his assailant, only to find that he actually recognizes them.

As this happens, an alarm sounds across the Seireitei and all captains are summoned to the First Division headquarters for an emergency meeting. Urahara groggily gets to his feet and hears that the Reiatsu of the Ninth Division task force has vanished. Concerned, he rushes into the laboratory and asks a researcher where Hiyori is. When she tells him that Hiyori has already left, Urahara rushes off, thinking to himself that he should have went himself and unable to comprehend that this is happening.

Aftermath
The Gotei 13 holds an emergency meeting upon the detecting the disappearance of the Ninth Division task force's Reiatsu. The Gotei 13 is forced to send an additional task force of five captain-level Shinigami to investigate the disappearances of the Ninth Division Shinigami. The Seireitei is placed on high alert as this crisis occurs. In addition, Kisuke Urahara and Tessai Tsukabishi end up heading to scene as well.