The Dissociation of Haruhi Suzumiya (涼宮ハルヒの分裂) (Suzumiya Haruhi no Bunretsu) is a Haruhi Suzumiya Light Novel.
As the second year of high school begins, Haruhi's cynical and sarcastic confidant Kyon, the only "normal" member of the SOS Brigade, finds himself meeting Sasaki, an old friend from his days in junior high. Haruhi and Sasaki's shared friendship with Kyon and, possibly, shared abilities, causes tension between the two and Kyon knows Haruhi's dissatisfaction can have dire consequences! Kyon and Sasaki's chance meeting could affect his future, the future of the SOS Brigade, and the world forever.
This ninth volume of the Haruhi Suzumiya series is the first to use two alternate stories for the same plot with different endings. The story continues in the next novel, The Surprise of Haruhi Suzumiya.
Kyon enters his second year of high school at North High and notices that the ordering of the classes is almost identical to the previous year; Kyon is still grouped with Haruhi in Class 2-5, while Itsuki is Class 2-9 and Yuki is in a separate class. Haruhi forces Mikuru and herself into cheongsams, while the president of the Student Council comes to investigate that the Literature Club is in session and not the SOS Brigade. (Haruhi, however, fools him by keeping a layer of wooden foil on top of a sign that says "SOS Brigade" to make it seem like it says "Literature Club".) The Computer Study Group president visits the SOS Brigade and tells Kyon that the few times Yuki visits she has been very helpful, fixing every bug and even creating a new OS that everything is compatible with. Haruhi announces her plans to film the sequel to "The Adventures of Mikuru Asahina Episode 00", "The Revenge of Yuki Nagato Episode 00".
Itsuki points out that Haruhi has become more unstable due to an incident that had happened earlier. As Kyon went to the train station, he met an old middle school friend of his, named Sasaki. Sasaki mulled over certain things in life, leading Kyon to believe she was much like Itsuki. The rest of the SOS Brigade appeared at the spot, and as Kyon introduced all of his friends to Sasaki, Haruhi became increasingly more irritable.
Kyon mulls over how he first met Sasaki through his cram school, and how they would often talk about trivial things like Kyon's name, and how they would ride on bicycle from middle school to cram school together and Kyon would escort Sasaki to her bus station.
On Saturday evening Kyon meets Sasaki again, only to find that the girl that kidnapped Mikuru in The Intrigues of Haruhi Suzumiya, named Kyouko Tachibana, is accompanying Sasaki. Incensed, Kyon tries to dissuade Sasaki from associating with Kyouko, but Sasaki tries to calm him down and introduces Kyon to another friend of hers, Kuyou Suou, a humanoid interface from an entity different from the Data Overmind (the Macrospatial Quantum Cosmic Existence, mentioned in "Snow Mountain Syndrome" and The Intrigues of Haruhi Suzumiya) with deficient communication skills (she can barely convey her own name), seemingly stemming from a lack of individuality. She tells Kyon that he has pretty eyes. Sasaki also reveals that she has been associating with the future man from The Intrigues of Haruhi Suzumiya, and tells Kyon she knows about their true identities; Kyon only confirmed it.
The SOS Brigade runs into Kyon, Sasaki, and her associates, and Kyon notices an amount of tension between Haruhi and Sasaki, Yuki and Kuyou, and Itsuki and Kyouko. Kyon goes home and gets a phone call. The plot splits from here:
The caller is a girl unknown to Kyon who does not even reveal her name, but sounds extremely familiar to Kyon. After saying some strange things (such as suggestion Kyon should not have forgotten her) and hanging up, the caller leaves Kyon very confused. Kyon calls Itsuki and asks about Kyouko and Sasaki's other associates, and Itsuki replies that even though they possess similar values as the SOS Brigade, Kuyou Suou presents a threat as nobody can understand her motives.
Kyon wakes up the next day, a Monday, and meets up with Haruhi, who tries to persuade him to take more action in brigade activities, because she is recruiting new members who may pass Kyon in seniority. Kyon also speaks with Yuki, who confirms that Kuyou's motives are unknown, but her faction was responsible for her illness in Snow Mountain Syndrome. She also explains that the Data Overmind has been able to give a more correct name to the Macrospatial Quantum Cosmic Existence, the "Sky Canopy Dominion", because they come from the zenith of the sky. This is apparently great progress.
At the end of class, Kyon gets help from Haruhi with some math problems in order to prepare for an upcoming math quiz, and Haruhi welcomes new first-year brigade applicants to the room, all of whom Itsuki confirms to have no extraordinary origin. Although Kyon counts eleven members at the beginning, someone slips in, changing the count to twelve. After Haruhi kicks out a potential member who comes only to find out what the SOS Brigade does, Haruhi declares that the SOS Brigade is meant to greatly enliven the world, and that all of the potential members are currently in an "entrance examination". Kyon notices there is one girl who is taking a great amount of interest in the Brigade and what it does, while Kyon experiences a nagging feeling that he's seen her before. Haruhi dismisses the new members, saying that anyone who wants to join the Brigade attend the next day, as she does not want anyone who bails to join her Brigade. As the first-years leave and Haruhi prepares a written examination, Kyon wonders who will return the next day.
The caller is none other than Sasaki, who invites Kyon to meet her, the time traveler man, Kyouko, and Kuyou at the café the SOS Brigade usually meets at Sunday morning. After Kyon hangs up, he calls Itsuki, who believes that Kyouko does not acknowledge Haruhi as a god and cannot enter closed space. Kyon also calls Yuki and asks if it is safe to attend the meeting, and she confirms it, also revealing to Kyon that the Data Overmind has created a more accurate name for the Macrospatial Quantum Cosmic Existence: the Sky Canopy Dominion.
Kyon attends the meeting at the arranged time, where he meets the time traveler man, who introduces himself using a fake name, "Fujiwara". Kyouko tells Kyon a shocking revelation: Kyouko's organization believes that Sasaki is the god and not Haruhi. Because Sasaki is not emotionally unstable, Kyouko believes that Haruhi's powers should be transplanted to Sasaki in order to avoid danger, even though Sasaki does personally not wish herself to be a god. To prove her point, Kyouko takes Kyon into Sasaki's version of sealed reality, which is actually a white version of the entire world where Avatars are completely absent. (However, Kyon notices that they are devoid of any change at all.) After Kyon and Kyouko return, they come upon Emiri Kimidori, who serves as the waitress at the café. Without warning, Kuyou grabs onto her wrists for no apparent reason at all, and abruptly leaves after letting them go. The meeting broke up over mutual disagreements, as only Kyouko was actually interested in transferring power to Sasaki; even Sasaki herself had little interest in this. Disoriented, Kyon leaves as well.
At school the next day, a Monday, Kyon thinks back to a conversation he once had with Sasaki about whether aliens, time travelers, or espers exist; Sasaki vehemently denies their existence and gives Kyon a logical argument as to why they cannot. When Kyon asks about what Sasaki thinks about attractiveness, Sasaki answers that she believes love is much like a mental illness (compare Haruhi's ideals) and is meant more for instinct as to preserve the human race.
Kyon goes to the clubroom and notices that nobody is there. Kyon notices that Mikuru is starting to look more like the future Mikuru he has seen in The Melancholy of Haruhi Suzumiya, and believes this signifies that he will be parting with Mikuru soon. Haruhi comes in and tells Kyon that she will be holding examinations for potential first-year applicants to the SOS Brigade. Itsuki also enters to play games with Kyon, but Yuki's absence does not go unnoticed. The Brigade looks everywhere for Yuki, including her classroom and the Computer Study Group room, but she is gone. Haruhi calls Yuki, and Yuki tells Haruhi that she has the flu, something Kyon takes to be unprecedented and believes is the responsibility of Kuyou Suou and the Sky Canopy Dominion, while Itsuki believes it to be the responsibility of the silicon lifeforms found in "Wandering Shadow". Kyon considers whether to use his trump card (telling Haruhi that he is John Smith) while Haruhi organizes the Brigade to set off for Yuki's apartment. As they get ready, Kyon makes a statement about Haruhi: "Members who dare to oppose this leader of ours do not exist at all."