[[quoteright:300:http://static.tvtropes.org/pmwiki/pub/images/koikaze.jpg]]
[[caption-width-right:300:Koshiro & Nanoka]]
After his girlfriend dumps him for someone else, 27 year old Koshiro has a chance encounter in the subway with Nanoka, a 15-year-old high school girl. He later meets her again at the entrance to an amusement park and since he has just been given two free tickets to it, he invites her to go with him. Each being rather depressed over the end of a relationship, they immediately feel some emotional connection across their age difference as the afternoon progresses.

On leaving the park, they suddenly discover that they are brother and sister when they both recognize and greet their father as he's arriving. This comes as quite a shock, since they haven't seen each other since their parents got a divorce with split custody some 10 years ago. Moreover, Nanoka is now moving in with her father and brother since their house is much closer to the high school she's attending. Against their better judgment, the first spark of mutual attraction slowly ignites into something deeper and more powerful as time progresses, especially since Nanoka develops a huge big brother complex and she is not deterred in the least by Koshiro's boorish and unsociable nature.

''KoiKaze'' started out as a manga series which then got adapted into an anime series in 2004 and immediately received a lot of attention for its harrowingly realistic examination of sibling incest. The painful and guilt-ridden romance between Koshiro and Nanoka is credibly full of angst and BelligerentSexualTension as the two struggle against their desires, refreshingly devoid of the blithe disregard for social mores and {{fanservice}} most {{shonen}} series on similar subjects tend to have.

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!!This series provides examples of:

* ArrangedMarriage: Koshiro works in an ''omiai'' (dating arrangement) office. He even faces the possibility of having one of these dates at some point. [[spoiler: He refuses]].
* AdaptationDistillation: The anime is very faithful to the manga, but it compresses the two-year period encompassed in the manga (three springs) to one year (two springs). Also, oddly, the events of the manga's second chapter were made into an unaired episode 8 of the anime, later restored to the DVD release.
** PragmaticAdaptation: While most of the events from the manga are still in the anime, they are shuffled around to better fit the anime format - some events from early in the manga happen very late in the anime, and vice-versa, which leads to those events having a different context because of how different the relationship between Koshiro and Nanoka is when they happen.
** All of the side characters have reduced roles in the anime, due to time constraints, and some side characters are even cut completely.
* BittersweetEnding: At the end of the anime, [[spoiler: Koshiro and Nanoka are together and happy, but there is unmistakable symbolism that, at the very least, they are still facing a very difficult time to come]]. The makers of the anime obviously wanted to make a point here.
** [[spoiler: The manga has some foreboding symbolism in the chapters leading up to it, but ends on a more positive tone, with Koshiro and Nanoka contemplating the inevitable challenges ahead (symbolized by the park where they "met" on the verge of closing) with open eyes and resolving to stick things out anyway]].
* BrotherSisterIncest: Goes without saying. One of the best deconstructions of the trope around.
** Something of a reconstruction too, as it presents a situation where the [[http://en.wikipedia.org/wiki/Imprinting_%28psychology%29#Westermarck_effect Westermarck Effect]] doesn't come into play.
** There's also [[http://en.wikipedia.org/wiki/Genetic_sexual_attraction Genetic Sexual Attraction]] to explain why they have such strong feelings towards each other.
* CherryBlossoms: You can't have a Japanese romance without 'em.
* ChristmasCake: Koshiro's family and coworkers wonder why a guy his age isn't married yet.
* ComicBookTime: Averted; Nanoka clearly grows older as time passes.
** [[spoiler: Koshiro's last words in both the anime and manga, said with an emotional expression that contrasts jarringly with his numbness at the series's beginning: "Love you.... I love you."]]
* DeliberatelyBadExample: Odagiri [[{{Ephebophile}} openly lusts for high-school-aged girls]] and sure wishes he could be in Koshiro's situation with Nanoka--which, of course, is exactly why he's not; he's mostly there just to remind us Koshiro is nothing like him and never asked for this whole situation to be foisted on him in the first place.
* DrivenToSuicide: [[spoiler: Nanoka at one point suggests committing lovers' suicide, but Koshiro objects. It seemed intended not to be taken too seriously, but her reason that it would much easier than trying to figure out their relationship implies she was at least half-serious.]]
** [[spoiler:Koshiro not replying to that suggestion immediately implies that he was also seriously considering it.]]
* EarnYourHappyEnding: [[spoiler: What Koshiro and Nanoka are still striving to do by the end.]]
* FerrisWheelDateMoment: In the first episode, before they knew they were siblings.
* FirstKiss: A bit ironic when Nanoka initiates a serious kiss with Koshiro and then ''she'' yells, "Aahhh! It's gone! My first kiss!"
* GallowsHumor: Most of the [[OnTheNext next-episode previews]].
* HardDrinkingPartyGirl: Chidori, who once partied so hard that she was calling herself "Midori" as she pressed more booze on Odagiri to get him drunk with her. In addition to drinking hard, however, she's also rather hard-bitten and sometimes gets rather mean when she's drunk.
* HiddenHeartOfGold: What Nanoka thinks Koshiro has. [[spoiler: She's not wrong, at least where she's concerned.]]
* HugeGuyTinyGirl: Koshiro's a big guy. Tall, heavy set. Nanoka, though almost 18 by the end of the series, is still tiny. He's well over a head taller than her.
** A bit less pronounced in the manga, since Koshiro is slimmer there.
* ImAManICantHelpIt: Invoked by Koshiro in a next-episode preview, where he uses this as an excuse for staring at Nanoka's underwear.
* InvulnerableKnuckles: Averted - In the manga [[spoiler: after Koshiro asks Chidori to start dating, she punches him in the face. Two pages later, it is shown that her knuckles are hurt as much as Koshiro's face.]]
* JerkAss: Koshiro for the most part, until [[spoiler: he and Nanoka decide to hell with everyone else, they will be together]].
* LoveBubbles
* LuminescentBlush
* MayDecemberRomance: Aside from being her brother, he's also twelve years older than she is.
* NoPeriodsPeriod: Subverted: Nanoka has her first period in three months and suffers some severe cramps from it.
* NotBloodSiblings: [[spoiler: Averted; though the series offers a few hints here and there that it's going to pull this particular cop-out and tell us Koshiro is actually adopted, it ultimately [[RedHerring pulls the rug out]] from under everyone wishing this were the case.]]
* SolomonDivorce: Nanoka and Koshiro are apparently only reunited for overall convenience.
* SurpriseIncest: They find out they're related before their first "date" is over, but they've already developed feelings for each other by then, even if they both try to pretend otherwise after the revelation.
* TakeThat: If his comments about wishing to have a cute little sister are any indication, Odagiri is this to people who would watch this show in hopes of it having incest {{Fanservice}}.
* TheChikan: Nanoka runs into one once on her way to school. It's not a major plot point, but it occurs shortly after Nanoka got into an argument with Koshiro because she felt he was being annoyingly overprotective of her, and the experience led her to appreciate that Koshiro meant well.
* UmbrellaOfTogetherness: Turns up in a couple of episodes, especially during the rainy season.
* VisibleSigh: Also makes an appearance or two. One humorous variation had a cloud forming over Nanoka's head and exploding with an audible pop when a boy mentioned rumors he'd heard that she had a brother complex.
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