Part of the reason to its popularity is because of Word of God claims it's biographical, and her anonymity makes the events of the story believable. This has been Retconned as being Very Loosely Based on a True Story, though there are rumors going on that it's Based on a Great Big Lie due its exaggerations and suspiciously strategic emotional appeal. Nevertheless, the success of Koizora led to a manga adaptation drawn by Ibuki Haneda, a theatrical film starring Yui Aragaki and Haruma Miura, and a television drama starring Erena Mizusawa and Koji Seto.
The story follows young Naïve Everygirl Mika Tahara, a girl who daydreams of love. Through a random encounter of phone calls, she meets Hiroki "Hiro" Sakurai, a delinquent boy who she is initially afraid of, and the two gradually fall in love. Do they live Happily Ever After? ... Not exactly, when challenges in their lives pop up and threaten to split the couple apart, including a sociopathic ex-girlfriend, an unplanned pregnancy, and the possibility of death. There's a lot of Tear Jerker moments, so get your tissue boxes ready.
This series contains examples of:
- Adapted Out: Tatsuya and Uta are removed from the film due to time constraints. People who have only watched the film might not even know that Tatsuya was the guy originally competing Hiro for Mika in the beginning of the story.
- All Girls Want Bad Boys: Hiro's pretty much a delinquent, but he's really a Nice Guy.
- Betty and Veronica: Tatsuya and Yu are the Betty and Hiro is the Veronica to Mika's Archie.
- Berserk Button: Don't try to hurt Mika or else you'll face Hiro's bout of Unstoppable Rage.
- Bittersweet Ending: Hiro dies during a routine check-up before Mika can say goodbye and Mika almost commits suicide, but after reading a posthumous letter from him she decides to live on for him, their late daughter, and to Mika's surprise, their new baby girl.
- Bowdlerise: The original novel was darker than the film adaptation. Of note is Hiro's abusive tendencies in the second part, where Mika is literally put in danger when he tries to get her to break up with him. (Inhaling chloroform, anyone? Pressing a cigarette to your arm?)
- Break Her Heart to Save Her: Hiro's reaction to finding out he has cancer is to emotionally abuse Mika and force her to break up with her so that she won't be in pain when she finds out.
- Break the Cutie: The series really does push how much pain Mika has to go through.
- Clingy Jealous Girl: Saki, Hiro's ex-girlfriend. This doesn't even begin to cover her. Hiring a bunch of guys to gang rape the girlfriend of the boy who recently dumped you, spreading rumors and becoming the direct cause of her bullying, pushing said new girlfriend down the stairs because she's pregnant with your ex-boyfriend's child...and the fact that she does all of this and virtually gets away with it.
- Compressed Adaptation: The film can generally be seen as this for the novel, as many of the characters like Tatsuya, Uta, etc. in the original story were left out due to time constraints.
- Cool Big Sis: Minako, Hiro's older sister, helps Hiro and Mika with their relationship and even helps get revenge on Saki after Mika is harassed.
- Delinquent Hair: Oh, so very much. Hiro and his friends have dyed hair and it's what scares Mika away from them at first.
- Domestic Abuser: Hiro starts to become emotionally abusive in the second part of the story, though he only pretends to be to get Mika to break up with him.
- Dogged Nice Guy: Yu loves Mika very much, but when Mika discovers Hiro has cancer, he is sympathetic to her and allows her to go back to him.
- Driven to Suicide: Mika attempts this several times, first time being right after she gets gang-raped. It doesn't make it any better when Hiro dies of cancer.
- Good Girls Avoid Abortion: Played straight with Mika. Subverted with Uta, who genuinely is a good girl but was forced by her boyfriend to get an abortion not once, but twice. Inverted with Saki, who was a jerk to Mika but keeps her baby when she gets pregnant.
- Harassing Phone Call: Saki sends a lot of these to Mika when she tries to do a Relationship Sabotage.
- He Didn't Make It: Hiro and Mika's baby dies when Mika has a miscarriage, and, later, Hiro dies in the hospital.
- Her Heart Will Go On: Hiro stays conscious long enough to see Mika run towards him, but he dies. Mika is very depressed at first and even contemplates suicide, but she ultimately realizes that Hiro would have wanted her to live. At the end of the story, she moves on with her life, pregnant with her child with Hiro.
- Huge Guy, Tiny Girl: Mika is often deescribed as tiny and cute, while Yu is very tall.
- I Want My Beloved to Be Happy: Hiro intentionally becomes an abusive boyfriend to convince Mika to break up with him, as he knows his days are numbered. Later, Yu heartbreakingly does this when he lets Mika return to a dying Hiro.
- Jerkass: Hiro in the second part of the story pretends to be a mean jerk to distance himself from Mika.
- Karma Houdini: After all the horrors Saki put Mika through, she never gets retribution in the end. The most "punishment" she got was Hiro's older sister cutting her hair in revenge, but other than that, she gets away with everything.
- Love Dodecahedron: It's a little confusing, since everyone's feelings change in the course of the story. Hiro and Mika obviously like each other. Saki likes Hiro. Aya and Nozomu date for a while until Nozomu develops a crush on Mika. Yu and Tatsuya also like Mika.
- Love Makes You Evil: Love Hungry Saki tries to pull a Relationship Sabotage on Hiro and Mika's relationship when they start going out.
- Mood Whiplash: Did you think it was going to be a light-hearted love story? Wait until you see what happens after Hiro and Mika get together.
- Murder the Hypotenuse: It might be unintentional, but Saki attempts this when she pushes Mika down the stairs. Mika survives, but her baby doesn't.
- Only Known by Their Nickname: Hiro is rarely called by his full name, Hiroki.
- Pet the Dog: Hiro gets such a moment in the final part of the story, where the audience realizes that he's dying of cancer.
- Poor Communication Kills: Had only Hiro explained to Mika that he had cancer...
- The Power of Love: How did Hiro find Mika after she gets gang-raped? "The Power of Love!"
- Race for Your Love: Mika makes one to Hiro near the end of the novel, only to find out halfway that He Didn't Make It.
- Rape as Drama: Mika gets raped by a group of men hired by Saki. This event alone causes Mika to have a Heroic BSoD and Hiro helps her through it.
- Second Act Break Up: Halfway into the story, Hiro breaks up with Mika after learning he has cancer and resolves to keep his condition a secret so she won't have to suffer.
- Second Love: Mika dates Yu after breaking up with Hiro, and he helps her move on from him. Mika eventually leaves him to spend time with Hiro after finding out he has cancer.
- Secretly Dying: Hiro discovering he has cancer sets up the second and final part of the story.
- Shout-Out: Mika sings "Who?" by Ayumi Hamasaki in the manga to affirm her love for Hiro.
- Smoking Is Cool: Hiro is seen as cool and he also smokes.
- Stock Shoujo Bullying Tactics: Saki gets in on bullying Mika by ganging up on her with her friends and Slut-Shaming her on every single chalkboard at school.
- The Topic of Cancer: Hiro is afflicted with cancer.
- Very Loosely Based on a True Story: The story is said to be based off a true story and the author's own experiences. However, one can't help but feel that it's a very embellished story.
