Itsuki Koizumi (古泉一樹)
Itsuki Koizumi
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 Surprise of Haruhi Suzumiya
Voiced by Daisuke Ono (JP)
Johnny Yong Bosch (EN)
Michail Kadanyn (RU)

Itsuki Koizumi (古泉一樹 Koizumi Itsuki) is the fifth person to join the SOS Brigade, 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 a polite manner and likes to go into long lectures and explanations with very expressive hand gestures.

In the light novels, he's described at being very bad at board games and cards, but in the anime it's Kyon who usually loses to him.


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 token "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. Sure enough, Itsuki reveals that he is an esper working for a group he refers to as the 'Agency'. Itsuki goes on, informing 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, of course, Haruhi Suzumiya. The reason behind Itsuki's smiling façade was to please Haruhi, and he urges Kyon to do the same.

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. Otherwise, Itsuki only watches from the sidelines and agrees to everything Haruhi says. In the same episode, due to his "distinguished service and dedication to the brigade," Haruhi Suzumiya promotes Itsuki Koizumi to Deputy Chief (Vice Leader).

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.

In The Dissociation, he met briefly with Sasaki and her faction members Kyoko Tachibana and Kuyou Suou. Koizumi said and did little, but Tachibana seemed delighted to have met him.



Shortly after receiving a phone call from a mysterious girl Saturday evening, Kyon contacted Koizumi. Koizumi already knew of Sasaki's group and wasn't surprised they would take action, although he believed the kidnapping in The Intrigues wasn't her idea and may have been a "weird idea" given to her by the time traveler. He said that Tachibana is rational, making her better than an ignorant ally.

He further informed Kyon that Tachibana's group was similar to the 'Agency', having similar interests but different explanations for them. He said he had faith that his abilities had come from Haruhi.

On Tuesday, he and Kyon had several discussions. In one, he told Kyon that incidences of closed space had been reduced, believing this was because Haruhi was recruiting new students for the SOS Brigade. In a later discussion, Koizumi suggested that perhaps he and Haruhi had been doing something like dating, which Kyon (who hadn't) strenuously denied. Koizumi told him it might be a good idea to do so, away from the rest of the Brigade, saying he wouldn't have anything against it. Kyon said that would be a disaster, Koizumi would have to fix the situation afterward, and that if he ever thought about it, he wanted Koizumi to literally slap him into being sensible. Koizumi said he would do so, but it was the opposite of what he wanted to see happen.

Koizumi also warned Kyon that he was getting too "close" to Nagato. For instance, because he saw the mysterious time traveler as his enemy, then so did Nagato. Nagato's illness might create an opportunity for this time traveler, who may have known of this beforehand.

The mysterious girl, Yasumi Watahashi, joined the Brigade. On Thursday, Kyon invited him outside for a fake game of baseball (so he could discuss things with him away from Haruhi and other members of the Brigade). Koizumi claimed that Yatsumi Watahashi was normal and had no organization backing her up. He suggested she had joined the Brigade because Haruhi wanted a new member. Discussing other matters, Koizumi said he didn't want to rely on knowledge from the future for reasons of pride, said their "enemy" was bigger and more powerful but he didn't want to be looked down upon, and he suggested that Kyon and Haruhi start over again like Adam and Eve. (Kyon didn't appreciate the suggestion.)

The next day Koizumi arrived late. Due to the Student Council President, he had to take care of certain things that no one else would do anymore. He noticed a flower that Yasumi Watahashi had left the day before, which she had obtained from the mountain near Tsuruya's house. He immediately took pictures of it, learning that it was an orchid.


In The Dissociation he spoke to Kyon after Sasaki called him to a meeting with her faction for the following Sunday morning. He said that Tachibana is from faction competing with the 'Agency', and that she could not enter closed spaces created by Haruhi. He also said that she and her group were not much different from the 'Agency', and had similar interests but different explanations for them.

He said that Tachibana would not do anything violent at the meeting, and that she actually disapproved of it, but believed the "honeyed words" of the time traveler.

In The Surprise of Haruhi Suzumiya, he states that he will do anything in his power to help Yuki out of her ill state.

When Haruhi told Kyon she wanted to take Nagato to a hospital, Kyon suggested she seek Koizumi's help instead (as Kyon feared the hospital could reveal Nagato's nature).

Combined Timelines

In The Surprise second volume, he's seen together with Mikuru (big), fighting against Fujiwara and Kuyou Suou in order to protect Suzumiya. Fujiwara wanted Kuyou to kill her, but Itsuki snapped, saying they mustn't look down on this time period's people and prepared to fight with him to protect her. Itsuki told Kyon to get Haruhi, since Kyon is the prince, thus should protect the princess.

At the end Kyon finally asked him if Sonou Mori-san is his superior in the 'Agency', since he addresses her with honorifics, but she doesn't. He just said that Mori-san is Mori-san and they can address her as they like, avoiding to answer the question clearly.


180px-Itsuki unleashing esper powers

Esper powers.

Itsuki claims to be part of an 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).

Esper power

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 unknown if these feelings relate to the real Itsuki. The real Itsuki, does, however, reveal to Kyon alone that he finds Haruhi "charming" and felt envious of Kyon when Haruhi stayed at his side the whole time at the hospital.

While Koizumi has suggested that Haruhi only listens to Kyon, Koizumi has occasionally convinced Haruhi about various things. For instance, at the end of Snow Mountain Syndrome, he convinced Haruhi that everything she had experienced was a hallucination prompted by being lost in the snow.


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 of Itsuki, they get along well as Yuki is silent unless asked something, Mikuru is usually acting as a maid or being harassed by Haruhi, and Haruhi just generally don't talk much other then club talk.

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. However, in the light novel series, he later expresses that being part of the SOS Brigade is "easier" for Mikuru as she 'doesn't need to change anything about herself,' and when Kyon mentions his previous stance on her, he outright tells him "You actually believed me?"

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).

He mentioned wishing to help her get new hobbies in Mystérique Sign, and supported Kyon (against Haruhi) when he told her she could visit the Computer Research Society in The Day of Sagittarius.

Alternate Itsuki


Alternate Koizumi

An alternate version of Itsuki Koizumi appeared in The Disappearance. He went to Kouyouen, which was a co-ed school in the alternate universe. This version wasn't an esper and had a crush on Haruhi Suzumiya. However, she had little interest in him. The Alternate Itsuki confessed that he has feelings for the Alternate Haruhi to Kyon straightforwardly, unlike its real version who didn't tell Kyon straightforwardly that he likes Haruhi, but instead dropping hints for Kyon.