Itsuki is Kyon's brother.Starting three years ago, as soon as he gained his ESPer abilities, he also lost the memory of being the brother of Kyon. Or, he didn't lose that memory but Kyon did - which makes his gay/bi advancements on him even creepier.
Istuki's eyes really are Always ShutThink about it. He's an Esper, isn't he? He's navigating psychically.
Itsuki is really GodThis is mostly based on how the "Kyon is God" theory has the problem of Kyon not saying he is, while there are the many problems with accepting "Haruhi is God" that the "Kyon is God" theorists have highlighted. In this case, the entire situation would be conducted by Itsuki for his own amusement; he prefers to stay on the sidelines and watch the love story that he has constructed for himself unfold, and probably take a Third-Option Love Interest for himself at the end. It is very likely that if this were true, Haruhi is in fact within the loop of aliens, time travelers, and espers and has been told that Kyon is God. The main problem with this theory is that it would lack the narrative coherence of Kyon or Haruhi being God.
The entire series is a Batman Gambit on the part of Itsuki, who not only is aware of the Fourth Wall but is also the true "God" of the show.Itsuki harbors a crush on Kyon; however, being aware of their existence as a fictional property, he knows that making the Ho Yay too obvious actually results in a lesser amount of fanwork. So he creates a cast to deflect most of the criticism from hetero guys with Moe Moe archetypes, while making the Tsundere female lead juuuuuuust unlikable enough so that anyone with yaoi tendencies will find her unsuited for Kyon. Thus, the amount of Itsuki/Kyon grows, encouraging the production of more fanwork, and allowing more hints to be dropped in the anime/novels/show itself, thus resulting in all those scenes where Itsuki gets to make Kyon uncomfortable. Supported by Itsuki's lame excuse that he's only doing it to ward off Haruhi's attention, as all the moments where he's expressing his fondness for Kyon take place away from Haruhi's eyes.
Alternate alternative: Itsuki is the slider, and Kyon is the esperItsuki has dimension jumping powers. In fact, his power to identify Haruhi's emotions could easily be related to the ability to see into Closed Space, and he could transform by moving himself slightly "out of phase" with the dimension he's in. Thus, all of Itsuki's powers are related to alternate dimensions and "esper" was just the label Kyon attached to him. Slider would be a better description of his powers.
Espers are lying about only having active powers in Closed SpaceWhich could explain the above non-Haruhi instances, this would also mean that Kyon's supposedly muggle friends are Espers. He does ask one if they're "special" and gets a laughing response that he's been infected by Haruhi. What Kyon doesn't get is a direct answer.
Itsuki is being Ambiguously Gay in the way he is as two different backup plans.Plan 1: In the event that Haruhi is a Yaoi Fangirl: Get Kyon used to the idea of being with Itsuki, to keep Haruhi entertained if she gets bored with Mikuru. (This works if Itsuki really does like Kyon, because he can say it's not just because of Haruhi when and if they have to placate her.) Plan 2: In the event that Haruhi wants Kyon: Back off and let her have him. If Haruhi doesn't think Itsuki's competition, he won't be eradicated. Secondary reasons may also exist (regardless of attraction) depending on how much Itsuki really knows. For example, if Mikuru falls for Kyon (or Itsuki) and Haruhi has shown attention for him, they can pretend not to be interested in girls while Haruhi isn't there without letting Mikuru know about Itsuki or Haruhi's powers. Related, if Kyon gets caught "flirting" with Mikuru like in the anachronic finale, he and Itsuki can improvise the same thing without making Itsiki's cues obvious to Haruhi, and later add If It's Haruhi It's Okay to Kyon's act if she is being posessive of him and not of Mikuru.
Itsuki Koizumi is the son of Japan's former Prime Minister Junichiro KoizumiAnd Itsuki's hair will grow to be as grand as Junichiro's.
Itsuki's Gratuitous English line in "Endless Eight"...Will be translated into Japanese in the dub. The dub writer will do the same thing he did with the "Naze? Why?" scene and make Johnny Yong Bosch say "Aishiteru" instead of "AI LAAV YUU".
Itsuki is the Big Bad.He is, in fact, the LEADER of The Organization. As far as we seen, he tends to be.....unreliable when it comes to talking. Maybe he wants to get rid of/hijack Haruhi's power. Or maybe he's just there for some lulz, sort of like Gin Ichimaru.
Itsuki is wrong: Haruhi wouldn't magically retcon him into being gay for Kyon... because she already did.As noted by many a fan, the majority of Itsuki's Ambiguously Gay behavior occurs when Haruhi isn't looking - just like all the supernatural occurrences. The one time when Itsuki admitted having a straight crush on Haruhi? In Yuki's retconned world where Haruhi had no reality-warping powers. Whether Itsuki isn't aware of this or does but is simply too embarrassed to admit it is still up in the air.
Itsuki is an Artificial Human created by the organization.
Itsuki is constantly testing Kyon by.......playing the board games. Those games he plays with Kyon are actually something of a disguised aptitude test, trying to investigate him further.
Itsuki did not exist three (or four) years ago and is not aware of the fact.He hints that he is interested in time traveling, even if he "canít see the past me". The reason Mikuru won't let him tag along (in addition to (1) Kyon finding him annoying and (2) a third traveler being completely pointless) is that as a time traveler, she knows that he doesn't exist. To reveal that wouldn't be good. The only grounds for this is that in all the time traveling arcs, we see past Yuki and past Haruhi. The only one we did not see is past Itsuki.
Itsuki is a Troll.
Itsuki was given his powers by the IDSE.
Itsuki's compliments have backfired.Haruhi is unable to accept compliments and so Itsuki's use of them drives her away into the arms of Kyon whose internal snarking seems more like the kind of silent support Haruhi seeks.
Itsuki has already told us that he is a time traveler.
The baseball tale was a fail for Itsuki's evil plan.On the way back from Apartment 505, Haruhi is leading Kyon somewhere and then Kyon stops her by being a jerk. (They were going to the wrong side of the tracks from either of their homes.) When Kyon returns home he finds Itsuki is surprised to see him back so soon. My suspicion is that Itsuki planted some super-romantic thing on Haruhi and was foiled by Kyon's blockheadness.
Nagato is Koizumi's mother.Blame Haruhi for this one.
Itsuki is KyonMaybe a Literal Split Personality thing, maybe something else, but Kyon's introduction did involve him saying he had wished to be an Esper,then decided he'd be better as the Esper's sidekick who didn't have to do all the work.
Itsuki was originally going to be the slider.Word of God says that Kyon was originally going to be an esper, if that is the case than what was Itsuki going to be? A second esper? I think not! The whole sliders thing that Haruhi mentions is just something that Tanigawa forgot to write out of the story, because Itsuki was the slider during early writing.
everything Koizumi said is something he thinks is trueHe just pretends that he might be lying in order to keep Kyon off balance and easy to manipulate.
Koizumi is in love with Haruhi and all his Ambiguously Gay behavior is just another way to keep Kyon off balanceHe occasionally says things that suggest that suggest he has feelings for Haruhi and he regularly says things have no apparent purpose other than confusing Kyon. He hides it because it makes it easier for him to ship Kyon and Haruhi. When he noticed that Kyon makes Haruhi's behavior more stable he probably decided that making his job easier was better than pursuing a relationship that he knew wasn't going to happen.
Koizumi's ambiguously gay behaviors are caused by HaruhiWe have seen that espers have some sort of link to haruhi's mental state, and if haruhi feels attracted to kyon then it stands to reason that some of the emotional resonance could affect the espers.
Koizumi only recently became the Leader of the OrganizationIn an earlier novel, he states that he would betray the Organization if it opposed the SOS Brigade, but of course that would never happen if he was its leader. Also, if he was always in charge, that would mean the Organization was originally run by a 12-year-old. Who the hell would agree to that?!