Kodansha began publishing bunkobon versions of the novels on October 13, 2006; as of July 15, 2014, all nine of the main bunkobon volumes have been released.
Kodansha mulai menerbitkan versi bunkobon dari novel No. 6 pada tanggal 13 Oktober 2006; pada 15 Juli 2014, seluruh sembilan volume bunkobon utama telah diterbitkan.