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Itsuki Koizumi (古泉一樹)
Itsuki Koizumi Profile.png
Age 16-17
Gender Male
Height 178 cm (5' 10")
Occupation Student (grade 11), Vice Commander, esper, member of The 'Agency'
Introduced In The Melancholy of Haruhi Suzumiya
Last Appearance The Intuition of Haruhi Suzumiya
Voiced by Daisuke Ono (JP)
Johnny Yong Bosch (EN)
Michail Kadanyn (RU)

"Sometimes I get the feeling that we're all just a bunch of clowns standing on our tiptoes at the edge of a great abyss..."
―Itsuki Koizumi

Itsuki Koizumi (古泉一樹 Koizumi Itsuki) is the fifth person to join the SOS Brigade who is recruited by Haruhi Suzumiya because he fit with her idea of a "mysterious transfer student", after he was transferred into North High.

He later reveals himself to Kyon as an esper, working for a group he only acknowledges as the 'Agency' (translated as The 'Organization' in the anime). Though he was sent to North High by the 'Agency' to observe Haruhi, he believes that it was Haruhi's will that really brought him there.


Itsuki has an unflappable polite and affable manner and likes to go into long lectures and explanations with very expressive hand gestures. However, after numerous hints to this extent, in "Love at First Sight" he confesses to his Kyon that his polite manner is an act, and underneath he is often stressed out or even angry.

He excels at academics. Heavily intellectual, he enjoys arguing contradictory theories for rhetorical purposes. He often tells Kyon that he was "just kidding" about a grave statement he made earlier, making it ambiguous whether the statement was one of those strictly-for-fun theories or he is simply trying to disclaim responsibility for leading Kyon's thoughts in a certain direction.

He's characterized as being very bad at board games and cards, though in the anime version of "Remote Island Syndrome Part 1" Kyon loses to him at "Old Maid".

Koizumi is regarded as very attractive by the girls at North High due to both his looks and his mannerisms (as mentioned in The Surprise, for instance).


Itsuki became an esper three years prior to his transfer into North High, and was quickly taken in by the 'Agency'. (According to Kyoko Tachibana, he in fact founded it.) Upon his transfer to the school, Haruhi "voluntarily arrested" Itsuki to be part of her SOS Brigade. As with Mikuru Asahina, who Haruhi considers the "cute mascot" of the group, she sees Itsuki as the "mysterious transfer student" of the group.

Having already heard from Yuki Nagato and Mikuru Asahina concerning their true identities (as an alien and time traveler respectively), Kyon approaches Itsuki about his true identity. Itsuki informs Kyon that the higher-ups in the 'Agency' believe that the world is simply a dream a certain being is seeing, who can only be described as God. This being is Haruhi Suzumiya. The reason behind Itsuki's smiling façade was to please Haruhi, and he urges Kyon to do the same. He often watches from the sidelines and agrees to everything Haruhi says.

Aside from giving Kyon advice, Itsuki does not play a major role in any of the events until "Lone Island Syndrome", in which he stages a murder case in order to entertain Haruhi. In the same episode, due to his "distinguished service and dedication to the brigade," Haruhi Suzumiya promotes Itsuki Koizumi to Deputy Chief (Vice Leader), much to Kyon's chagrin.

In The Disappearance of Haruhi Suzumiya, when Yuki creates an alternate world in which Itsuki is a normal human, he reveals that he has feelings for Haruhi and also states that he feels jealous, due to Kyon's relationship with Haruhi. In "Snow Mountain Syndrome", he helps Kyon solve a puzzle to get out of the house and save Yuki.

It is revealed in "Editor in Chief★Straight Ahead!" that Koizumi is the puppetmaster behind the new Student Council President, who he put into power in order to serve as an adversary for Haruhi to focus her energies on.

In The Dissociation, he meets briefly with Sasaki and her faction members Kyoko Tachibana and Kuyou Suou. Tachibana seems delighted to have met him.

Season 1 artwork

In The Surprise, in both the α and β timelines, Koizumi reveals he already knew of Sasaki's group and isn't surprised they would take action, although he believes the kidnapping in The Intrigues wasn't her idea. He says that Tachibana is rational, making her better than an ignorant ally. Tachibana's group is similar to the 'Agency'.

After the timelines merge, he and Mikuru (big) use his esper power to enter the closed space in which Kyon and Haruhi have been trapped and help them fight against Fujiwara and Kuyou Suou.

Kyon asks him if Sonou Mori-san is his superior in the 'Agency', since he addresses her with honorifics, but she doesn't. He just says that they can address her as they like, avoiding answering the question clearly.


Esper powers.

Itsuki claims to be part of a group called The 'Agency' that consists of espers who work together to fight off celestials and repress Haruhi's creation of closed space. As an esper, he can use psychic, supernatural powers, but generally only in the closed space (beyond being able to sense supernatural phenomena).

Koizumi uses an energy sphere

In the anime, his powers derive two special attacks, named "Second Raid" and "Fumoffu", names of the two sequels of the Full Metal Panic! series. In the novels, his "attacks" are unnamed.

Relationships with SOS Brigade members

Haruhi Suzumiya

His attitude towards Haruhi is ambiguous, given that he agrees to everything Haruhi says to keep her happy; however, in The Disappearance of Haruhi Suzumiya, the alter-Itsuki reveals that he has feelings for Haruhi. It is implied that these feelings to at least some extent relate to the real Itsuki, since the alternate Itsuki explains his feelings by saying he finds Haruhi "charming", echoing a comment the real Itsuki made in The Melancholy, and the real Itsuki in turn echoes the alter-Itsuki's remark "Makes me jealous..." when Haruhi stays at Kyon's side the whole time at the hospital.

While Koizumi has said that Haruhi only listens to Kyon, she does accept Koizumi's suggestions in cases where they conform to her own desires.


Itsuki considers Kyon a trustworthy place to give information, but often invades his personal space. He often seems disappointed by Kyon's nonchalant or irritated attitude. Itsuki has even complained that Kyon's attitude toward him resulted in mockery at "the office". Socially specking, despite Kyon's annoyance and mistrust of Itsuki, they get along well. As the only two males in the club, they relate to each other in ways that they cannot with the other members.

Koizumi takes a keen interest in Kyon's relationship with Haruhi, rarely missing an opportunity to suggest a romance between them, sometimes jokingly, other times more seriously. In The Surprise, he directly suggests that Kyon ask Haruhi out on a date, and says that he hopes for a relationship to start between them. He believes Haruhi only listens to Kyon and expects him to "stabilize" her emotions in order to prevent the creation of closed space.

In The Intrigues and Random Numbers he admitted being envious about Kyon's time traveling trips, having taken a lot of interest in them, and complaining that Kyon would do things without him.

Koizumi offered to turn Kyon into an esper (which Kyon firmly turned down). He also mentioned how he was spending less time helping Kyon with various Haruhi-related problems, but (along with other 'Agency' members) helped him when Mikuru was kidnapped by a rival organization.

Mikuru Asahina

Itsuki believes that the older Mikuru Asahina can not be trusted, but is willing to come to terms with her. He also apparently distrusts the younger Mikuru, believing she created a pleasing helpless facade to manipulate Kyon. In "Love at First Sight", he backs away from this claim, leaving Kyon to doubt whether he was telling the truth or not.

There is also slight hostility between them as their factions have contradicting theories about Haruhi.

Yuki Nagato

Itsuki is able to track Yuki's development, although apparently not to the same extent as Kyon. Kyon noticed that Koizumi follows Nagato's every move.

He mentioned that Yuki rarely responds to his inquiries, but she often follows his instructions (which are based on Itsuki having a fairly high amount of knowledge of her abilities), such as getting her to destroy a fence in The Sigh or keeping track of time in Snow Mountain Syndrome. She sometimes answers factual questions which are beyond Kyon (most notably in Mystérique Sign, in which he mentions wishing to help her get new hobbies).

Other versions

Alternate Itsuki

Alternate Koizumi

An alternate version of Itsuki Koizumi appears in The Disappearance. He goes to Kouyouen, which is a co-ed school in the alternate universe. This version isn't an esper and has a crush on Haruhi Suzumiya. However, she has lost interest in him by the December day on which the world was altered. The Alternate Itsuki confesses that he has feelings for the Alternate Haruhi to Kyon straightforwardly, unlike the original version.

The Disappearance of Nagato Yuki-Chan

In the alternate universe spinoff The Disappearance of Nagato Yuki-Chan, Koizumi is a normal human attending Kouyouen just as in the alerted universe from The Disappearance of Haruhi Suzumiya, but his obsequiousness to Haruhi is much more pronounced, despite his not having to worry about her destroying the world. He unquestioningly answers Haruhi's every whim solely out of romantic attraction to her, even though (as he tells Kyon in "Haruhi Suzumiya", the first episode he appears in) he holds no hope of her ever returning his feelings. His role in this series is extremely small compared to his role in the original series, with him serving almost purely as comic relief.


  • The name Itsuki means "one" (一) (i) and "tree" (樹) (tsuki).
  • Itsuki's surname Koizumi means "old" (古) (ko) and "spring, fountain" (泉) (izumi).


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