The cell phone short story Koizora: Setsunai Koi Monogatari (恋空～切ナイ恋物語) was written by Mika, with 25 million readers by the end of the serialization. It was later published as a novel which sold approximately 2 million copies. The film adaptation was released in November 2007, with a gross revenue of 3.9 billion yen, with 3.14 million people attending the theater. The DVD was released on April 25, 2008.

The short story was also adapted into a TV drama series, which aired from August 2 until September 2008, with a total of six episodes. From March until June 2008, auditions were held to choose the actor and actress for the two starring roles. Erena Mizusawa was chosen to play Mika, and Koji Seto as Hiro; there were a total of more than a thousand applicants. TBSbroadcast the serial drama in prime-time, and the first audience rating was 5.6%.

The non-fiction story has recently been adapted into a manga series.

Koizora tells the story of Mika, living a simple school girl's life and the dramatic transformation that it undergoes when she meets Hiro, a student also at her school who is keen to call her his own. Mika was an average high school girl until she met Hiro during a scam to find her cellphone.



They talk on the phone all through summer vacation and later succeed their relationship as lovers. Hiro has led a very different lifestyle from Mika. His ex-girlfriend, Saki, is jealous of Hiro's new found love and arranges Mika to get raped. Hiro is angry about this incident and promises to protect Mika whatever happens.



Mika later gets pregnant with Hiro's baby and decides to marry him and have the baby. However, during a fight with Hiro's ex-girlfriend, the baby is gone. After that incident, Hiro dumps Mika and ignores her. Later Mika attends a Christmas party with her friend and college people. There, she meets another guy and they start going out with each other. Mika and Hiro meet at the place where they annually come to remember their deceased baby and Mika notices he is wearing a hat for the first time. The next winter, instead of Hiro, Hiro's friend shows up and tells her that Hiro is diagnosed with cancer, which was the reason he dumped her. Mika runs to the hospital and promises Hiro that she'll never leave him again.



Her relationship with her second boyfriend ended there. Hiro and Mika have a wonderful time for a while, and sometime later, Hiro asks Mika to print out some pictures for him. While she does that, Hiro had a really serious situation and died while in a phone call with Mika. Mika runs and then she falls and the pictures she had printed scattered everywhere. Suprisingly, all the pictures were of Mika and she cries.

Later, Mika tries to kill herself by throwing herself out of a bridge, but a dove comes out of nowhere and she freaks out, causing her to jump backwards and ends up not killing herself. She was holding Hiro's journal, and the journal magically opened to the page where he drew a picture of him, her, and their baby. The movie returns to the present because all this was Mika remembering Hiro while in a train like maybe 5 years later. She meets her parents at the subway station and they leave.