長鴻出版社
Written and illustrated by Kotomi Aoki, "Boku wa Imōto ni Koi o Suru" were originally serialized in Japan in "Shōjo Comic". The individual chapters were collected and published in ten "tankōbon" volumes by Shogakukan, with the first volume released May 26, 2003; the last volume was published on August 26, 2008. The series is licensed for regional language releases in France by Soleil Productions under the English title "Secret Sweetheart", in Spain by Editorial Ivrea, and in Taiwan by Ever Glory Publishing. The original volumes were also imported to the United States and sold as is by Borders and Waldenbooks bookstores in early 2005. In March 2008, to celebrate its 40th anniversary, "Shōjo Comic" posted free chapters of "Boku wa Imōto ni Koi o Suru" on its website, along with a new side-story.