The following article is a timeline of The Melancholy of Haruhi Suzumiya.
The general timeline begins approximately three years prior to the beginning of "Bamboo Leaf Rhapsody" (that point is referred to as year -3). The series itself starts in April of year 0. Timeline information is derived from the light novels and The Observation of Haruhi Suzumiya, the latter includes a timeline of the first year in high school.
The Melancholy of Haruhi Suzumiya features a number of stable time loops.
The future appears to be malleable, according to Mikuru Asahina, whose job is to protect the future she came from. Another time traveler faction, represented by Fujiwara, is irritated that they cannot change the future, although he has made attempts to do so.
Major Time LoopsEdit
One time loop extends from three years before the start of the series to The Disappearance of Haruhi Suzumiya. Four years ago, a frustrated Haruhi Suzumiya created a timequake, supposedly resulting in the creation of espers and drawing the attention of the Data Overmind. The timequake prevented time travelers from traveling before this point as well. This event seems to have sundered the timelines of Fujiwara and Mikuru Asahina; the former considers the latter his sister, but the latter says she has no brother.
On Tanabata of the series' first year, Mikuru Asahina took Kyon with her to three years prior (year 0). Kyon met with adult Mikuru, who gave him an assignment: help young Haruhi. She also disabled young Mikuru's TPDD. Kyon did as instructed, introducing himself to Haruhi as "John Smith". She noticed his North High uniform, and Kyon indirectly convinced her to go to that school. After leaving her, Kyon and Mikuru found themselves stuck in the past. Kyon took young Mikuru to see Yuki Nagato, who "froze" them in time three years until the "present day".
On the morning of December 18th, Yuki Nagato "stole" Haruhi's powers and rewrote the history of the world for the previous year and altering everyone's memories—even hers—but not Kyon's. (She also turned herself into a human.) This act created a timequake more powerful than the one generated by Haruhi. Nagato left behind an Emergency Escape Program if Kyon wished to revert the changes. Kyon eventually did, three days later. The program sent him back to the original Tanabata. He met adult Mikuru, who apparently had not yet left that time period. She told him to give another message to young Haruhi, and then they met at Nagato's apartment again. There Nagato revealed the culprit of the time manipulations was her future self. She gave Kyon a device to convert this Nagato back into a humanoid interface, then had Mikuru take him back. She could not go herself, as she had to oversee the "frozen" Kyon and Mikuru.
When he arrived back on the dawn of December 18th, Kyon had been told by the previous version of Nagato that he had to wait for Nagato to convert the world before curing Nagato. Kyon was interrupted by Ryoko Asakura, who nearly killed him with her knife. As Kyon fell, he was rescued by another Nagato... and himself. The "future" Kyon gave him a message. "Present" Kyon's injuries were later explained as him falling down the stairs. Kyon lost consciousness for three days. His memories of December 18th to 21st were significantly different from those of Haruhi, young Mikuru and Itsuki Koizumi.
On January 2nd of the following year, Kyon took Mikuru to Nagato's apartment. The three traveled to the previous December to save Kyon's life and put the world right. Nagato herself converted her previous self from a human to an interface.
According to Koizumi, the world changed significantly on December 18th, calling that point in time "X", and the time after the world was fixed "X*". Because Kyon did not stop Nagato from changing the world, only "resetting" it, "X" still exists, and has simply been "covered up".
The events of The Dissociation and The Surprise involve a timeline branching, called α and β, revolving around Haruhi "splitting" reality, apparently as a result of her becoming worried about Nagato's illness starting Saturday. In both realities, a younger version of Haruhi called Yasumi Watahashi was created.
That same day, Kyon got a phone call. In the α timeline was from Yasumi, although Kyon had never met her and so didn't realize who she was, whereas in the β timeline, he got a call from his old friend Sasaki.
In the end the two timelines were merged, leaving some confusion among people who had combined their alternates.
Koizumi and Kyon definitely combined as the timelines converged, but Koizumi could not be sure about other people. He believed the current Haruhi was the α version, but she demonstrated memories from both timelines. For instance, she recalled Yasumi joining the Brigade (α, but also Nagato's illness β. The orchid that Yasumi had obtained, only brought in the α timeline, was still there.
Koizumi believed that only the Brigade, Taniguchi, Kunikida, Sasaki and Tachibana noticed the timeline split (suggesting they had all combined their selves/memories).
Minor Time LoopsEdit
When Kyon first met adult Mikuru, she told him about the mole on her breast, saying Kyon had told her about it. Kyon, however, had yet to notice this and hadn't told her this from his perspective. Afterward he investigated photos of Mikuru, and noticed the mole. Only then did he tell her, which is how adult Mikuru became aware of it. This enabled Kyon to detect the false Mikuru in Snow Mountain Syndrome.
The world was caught in over 15,000 two-week-long stable time loops due to Haruhi's subconscious over the August vacation. The SOS Brigade (except Haruhi) would notice the loops many times, and Nagato was completely aware of them, but would take no action against it. In addition, Mikuru could not use time travel. Kyon eventually resolved the loop.
In The Sigh of Haruhi Suzumiya, Nagato had to repeatedly inject Asahina with nanites to keep her from making unintentional reality-altered attack. In The Disappearance, Nagato needed to do this to Adult Asahina again three years in the past (from Kyon's perspective). When Asahina mentioned how she was sorry she'd made Nagato do that "in the past" (during The Sigh), Nagato replied that for her, this was the first time she would do so.
In The Melancholy of Mikuru Asahina, a rival time traveler tried to kill a child. Mikuru (small) arranged for Kyon to rescue him from murder and later Mikuru (big) arranged for Kyon to inspire his vision of time travel. Mikuru (big) revealed that in the future, Haruhi would invent some of the theory behind time travel, and so would the boy. If it wasn't for Mikuru's faction's interference, the boy would not have grow up to develop his own contribution to time travel.
A coalition of opponents led by Fujiwara, a rival time traveler, and Kyouko Tachibana, a rival esper, conspired to kidnap Mikuru Asahina in February of year 1. Mikuru avoided this problem by jumping back in time eight days, creating two of her for that time period. Kyon and Nagato were assigned to assist "Michuru", as this version was called, from meeting her other self. Fujiwara attempted to prevent "Michuru" from taking a piece of time travel technology, but then let them have it. Later the enemies kidnapped "Michuru" but this was foiled by the 'Agency'. The enemies vanished in front of Kyon, complaining that the future could not be changed.
At the same time, Kyon was instructed by Future Mikuru to find the Bespectacled Boy and throw a turtle into the cold water in front of him. The vision of the ripples would eventually lead the boy to invent the TPDD in the future. As apparently the boy would not have made his invention without Kyon's inspiration, this creates a time loop.