Introduction: One day, I – a high schooler – found a paperback in the hospital. The “Disease Coexistence Journal” was its title. It was a diary that my classmate, Sakura Yamauchi, had written in secret. Inside, it was written that due to her pancreatic disease, her days were numbered. And thus, I coincidentally went from Just-a-Classmate to a Secret-Knowing-Classmate. It was as if I were being drawn to her, who was my polar opposite. However, the world presented the girl that was already suffering from an illness with an equally cruel reality…The best-selling, award-winning debut work by Yoru Sumino:“Bestsellers 2016 (Overall) by NIPPAN” – 4th Place“Bestsellers 2016 (Paperback Fiction) by NIPPAN” – 1st Place“Bestsellers 2016 (Overall) by TOHAN” – 5th Place“Bestsellers 2016 (Literary Books) by TOHAN” – 1st Place“Bookstore Grand Prix 2016” – 2nd Place“DA VINCI BOOK OF THE YEAR 2015” – 2nd Place“Bestsellers 2015 (Literary Books) by TOHAN” – 6th PlaceAs of May 2017, this book has sold over 1.2 million copies....