The SOS Brigade is a club to investigate mysterious events. Among the members of the SOS Brigade are:

Kyon (???)

Voiced by: Tomokazu Sugita (Japanese); Crispin Freeman (English)

The primary narrator and main protagonist of the series. While his real name is never given, everyone calls him by his nickname "Kyon", given to him by his younger sister. Kyon is a high school student with a laid back and sarcastic attitude. He unintentionally runs into Haruhi and is the only normal human in the SOS Brigade. Even though Haruhi is the title character, the story is told through Kyon's viewpoint. Through narration and dialogue, he provides his insight, perspective, and opinions on events. Kyon is often annoyed by Haruhi's demands but thinks that a world without her would be uninteresting. Kyon is also "John Smith" from Haruhi's earlier memories and was the one who painted the hieroglyph in the field. Very early on, Yuki, Mikuru and Itsuki revealed what they are to Kyon, after which, they begin on many journeys throughout time and space. In an interview with Nagaru Tanigawa, the author admitted that Kyon was supposed to be portrayed as an esper in his original conception, but while writing The Melancholy of Haruhi Suzumiya, Kyon was instead changed into an ordinary student. He is the main character of the spin-off series The Disappearance of Nagato Yuki-chan. He met Haruhi at that time, four years ago helping her draw the message in her school while naming himself "John Smith" but does not remember. In The Surprise of Haruhi Suzumiya, Kyon time leaps and briefly meets a college-age Haruhi with another version of himself on campus where the two appear to be close.

Haruhi Suzumiya (?? ???, Suzumiya Haruhi)

Voiced by: Aya Hirano (Japanese); Wendee Lee (English)

Haruhi Suzumiya is the title character, the main female protagonist of the series, and leader of the SOS Brigade whose energetic and eccentric character proves to be the driving force for the series. She has a mind for adventure which often leads her subordinates to be swept into her plans. While being smart, beautiful, and energetic Haruhi was eyed as an oddball ever since middle school: She set all the desks from her classroom out into the hallway, painted stars on the roofs, and even painted a huge hieroglyph on the school field (though this was later shown to be Kyon). Haruhi cannot stand boredom so she comes up with activities for the SOS Brigade, making them participate whether they like it or not. In the sixth grade, Haruhi felt she was no longer special after going to a baseball game and realizing she was one in a sea of people. After that she set out to make her life interesting and unique. What Haruhi does not know is that she has an outstanding power to change the environment around her as she pleases. By subconsciously using it, she gathers Mikuru Asahina, Itsuki Koizumi, and Yuki Nagato into one place: the SOS Brigade. The story is indirect in saying how much Yuki, Mikuru and Itsuki know about each other.

In an interview, Tanigawa stated that the idea for the character came during a sleepless night at the beginning of the 21st century. Haruhi is considered to have tsundere character traits but is perceived by some as "too energetic" to be a true tsundere. Erin Finnegan of PopCultureShock compared her outlook to that of Fox Mulder from the X-Files, as Haruhi, too, "wants to believe." Unlike Mulder, Finnegan describes Haruhi as an "immature, self-centered tsundere with violent mood swings." One of the anonymous Tiger Mask donations was signed "Haruhi Suzumiya."
IGN ranked her as #19 on their list of top 25 anime characters.^[6] She is an important character in the spin-off series The Disappearance of Nagato Yuki-chan. She retains her character from The Disappearance of Haruhi Suzumiya in which she has no powers to alter reality, but and is a normal high school girl who attends Kouyouen Academy with Itsuki Koizumi. She retains her goal of finding aliens, time travelers and espers, as well as her energetic and eccentric character. She met Kyon at that time, four years ago with Kyon drawing the message for her in her school; she might have fallen in love with Kyon after she remembers and recognizes Kyon as John Smith in her earlier memories.

Yuki Nagato (?? ??, Nagato Yuki)

Voiced by: Minori Chihara (Japanese); Michelle Ruff (English)

Yuki Nagato is a bibliophile humanoid interface that was created by the god-like figure called the Data Integration Thought Entity. Yuki's responsibilities involve monitoring Haruhi and the investigation of an unexplained "explosion of data" three years before the present story. She possesses an ability to manipulate her surrounding environment, or "data" as quoted by her. Yuki is very quiet but can speak at length when it has to do with her mission or a problem that has arisen. While she always seems to be engrossed in her reading, she comments that she is only relatively interested in them. Yuki gives hints and aid to Kyon throughout the series. She almost never shows any emotions, but there are times when she shows interest in things, such as programming computer games and playing them, as well as reading (in the light novel The Disappearance of Haruhi Suzumiya it is further revealed that she may have developed an interest in writing).

It is revealed in The Disappearance of Haruhi Suzumiya novel and film that she does develop emotions. In her context, developing emotions is like accumulating error data which will cause a bug to trigger anomalous behavior. The unpleasant emotions developed throughout the series (caused by the people around her) makes her wish for a normal world, whereby she finally takes action in The Disappearance of Haruhi Suzumiya. Yuki is well-acquainted with time travel and that Mikuru is a time traveler. Mikuru and Itsuki are aware that Yuki can do amazing things but know far less about it than Kyon does. She is also the main heroine of the spin-off series The Disappearance of Nagato Yuki-chan. She retains her character from The Disappearance of Haruhi Suzumiya in which she is not an alien — she is a shy girl who has a crush on her fellow literature club member, Kyon. She had an accident, a near-hit with a car that possessed her with a different personality having the quiet and stoic character in The Melancholy of Haruhi Suzumiya. With her inevitable disappearance drawing near, she confesses to Kyon before she disappears with the other Yuki taking her place.

Mikuru Asahina (??? ???, Asahina Mikuru)

Voiced by: Y?ko Got? (Japanese); Stephanie Sheh (English)

Mikuru Asahina is a time traveler from the distant future who is assigned to investigate the reason behind the inability to travel to any point before three years before the present story. Mikuru is a soft-spoken girl who almost always willingly follows Haruhi's demands. She is the lowest in her Time Travelers' Committee. She often tries to explain what is going on but heavily censors it by saying "classified information." Haruhi loves dressing up Mikuru in (sometimes embarrassing) outfits, claiming that she is the "mascot" of the SOS Brigade. Kyon appears to have a bit of a crush on her (this is somewhat more apparent in the novels, as are Mikuru's feelings for Kyon). For her part, Haruhi seems quite jealous of her and Kyon's relationship. In the anime and novels Mikuru discourages Kyon from acting upon any feelings that he may have for her, explaining that he is Haruhi's "chosen person." In The Boredom of Haruhi Suzumiya light novel she implies that if he is nice to her, bad things will continue to befall her. She has told Kyon that Yuki and Itsuki are like herself, but when Kyon asks her if she knows what they are she answers "That's classified information." She is also a supporting character in the spin-off series The Disappearance of Nagato Yuki-chan in which she is not a time traveler but retains her character from The Disappearance of Haruhi Suzumiya.

Itsuki Koizumi (?? ??, Koizumi Itsuki)

Voiced by: Daisuke Ono (Japanese); Johnny Yong Bosch (English)

Itsuki Koizumi is an esper who, like the other members of "The Agency," suddenly acquired three years before the present story the power to explore the "Closed Space" and combat Celestials that Haruhi Suzumiya creates when she is unhappy. He is fairly carefree and always smiling. Kyon seems to be annoyed by him and, in the light novels, expresses his urges to hit him. Itsuki brings up many points that have multiple sides, and. He explains to Kyon that Mikuru, or anyone, could be putting up a fake personality and deceiving everyone. In the first volume he states that Yuki is an alien and Mikuru is a time traveler, but then mentions the theory that he and they are what they are because Haruhi wants aliens, time travelers and espers to exist. He remarks that Kyon is the biggest mystery because as far as anyone in the Agency can work out, Kyon is totally normal, yet Haruhi is interested in him. Yuki and Mikuru are somewhat aware of what Itsuki's role and concept is. They have Itsuki convey messages to Kyon when Kyon and Haruhi vanish from this world into a closed space. He is also a supporting character in the spin-off series The Disappearance of Nagato Yuki-chan in which he is not an esper, but a normal high school boy who attends Kouyouen Academy with Haruhi Suzumiya. He retains the same character he had in The Disappearance of Haruhi Suzumiya where he is in love with Haruhi.

Yasumi Watahashi (?? ??, Watahashi Yasumi)

She briefly joins the brigade in the tenth novel, claiming to be a first-year student at North High. She is instead a literal deus ex machina, created by Haruhi to block Sasaki's interactions with Kyon. When the crisis is resolved, she disappears from existence with Haruhi believing she was a middle school student who sneaked into the brigade.

Ryoko Asakura (?? ??, Asakura Ry?ko)

Voiced by: Natsuko Kuwatani (Japanese); Bridget Hoffman (English)

At first, Ryoko appears to be a compassionate and hard-working high school girl. One of Kyon's friends, Taniguchi, places her in the top three first-year girls in the school with a grade of AA+: indicative of her pleasant personality, beauty, and athleticism. Her enormous popularity made her the unanimous choice for class president of Kyon's homeroom class. She showed particular concern about how Haruhi had distanced herself from the rest of the class.

It turns out that she is Yuki's backup and, as such, is another "humanoid interface." Much like Yuki, she finds it difficult to empathize with humans. Unlike Yuki, she possesses exceptional social skills. Initially she cheerfully supports Kyon's reaching out to Haruhi, often encouraging him to "open her up to the class," making Haruhi easier to observe. However, when Haruhi brings up the idea that someone disappearing would be interesting, it gives her the idea to try to kill Kyon (since Haruhi seems to care a lot about him) with a combat knife in the hopes of catalyzing an observable reaction from Haruhi. In battle, she mainly excels in controlling a select amount of data, making her own type of closed space, and hand-to-hand combat. Her efforts are stopped, after Yuki defeated and removed her from the physical world. Her cheerful personality doesn't falter, even at the moment of her own demise. This is a clue given by the author that Ryoko really did not understand the concept or the heavy implications of death, either her killing Kyon or her own death; that in the end, what she did was the result of simple logic that if Kyon were to have died, then Haruhi would give a reaction, not for the purpose of bloodlust. Ryoko is often called a yandere by fans. Afterwards, Yuki fabricates a cover story that Ryoko moved to Canada.

She makes a reappearance in the light novel The Disappearance of Haruhi Suzumiya, on an alternative timeline in which Haruhi never attends North High or forms an SOS Brigade. It is revealed that she cares deeply and is best friends with the alternate Yuki but would resort to violence to protect her. She stabs Kyon when he tries to inject an un-installation program into Yuki. She is stopped and destroyed by another Yuki that came from a few months later, along with Kyon and Mikuru, to save him. She appears again in book 10, The Astonishment of Haruhi Suzumiya, preview released in 2010, when Kyon encounters Kuyoh Suoh, another humanoid data interface created by the Macrospatial Quantum Existence, or "Canopy Dominion" at the train tracks to save him. Her main duty is to appear whenever there is an emergency when Yuki is not available. Their fight is interrupted by Emiri Kimidori, another humanoid data interface created by the Integrated Data Sentient Entity, while Asakura was thrusting her combat knife at warp speed. She notes that Kuyoh does not ask for any permission to alter data and escapes the closed space. She disappears once again, but a note is taken that Asakura will appear when necessary. She appears hostile, telling Kuyoh that Kyon is her "prey."

In the spin-off mini-series The Melancholy of Haruhi-chan Suzumiya, she appears as a chibi form dubbed 'Achakura' as a basketball-size result of a failed reincarnation and is forced to help Yuki around her house. She is subject to pranks from Yuki, such as being transported around in a baby carrier or dressed up like a Hinamatsuri doll. In Nyor?n Churuya-san, her appearance is similar to Tsuruya/Churuya and she has a crush on Kyon. She is one of the main characters in the spin-off manga, The Disappearance of Nagato Yuki-chan, retaining her character from The Disappearance of Haruhi Suzumiya.

Tsuruya (??)

Voiced by: Yuki Matsuoka (Japanese); Kari Wahlgren (English)

Tsuruya is the hyperactive friend of Mikuru (from the current time plane) notable for her loud voice, knee-length hair, and prominent tooth. She has a cheerful and friendly disposition. She is prone to long fits of unrestrained and intense laughter at things she considers even the slightest bit humorous.

Her fang-like tooth gives her an idiosyncratic speech pattern, causing her to misspeak by leaving out syllables. Her speech pattern is often accompanied with a lisp and her catch phrases "megas" and "nyoro". She was named "honorary consultant of the SOS Brigade" by Haruhi. She is the heir of the Tsuruya family, which purportedly collaborates with Itsuki's Agency. It is unknown if Tsuruya has a secret identity or agenda.

Though not a member of the SOS Brigade, she plays a minor role in The Adventures of Mikuru Asahina Episode 00 and serves on their baseball team in episode four. She has a small appearance in the ninth and twelfth episodes but otherwise appears relatively sparingly throughout the anime. She appears a few more times during the novels — more prominently than in the anime's rendition of the same stories and even get