Apparently all of the chapters in this manga (save for the 9th) are from past manga. This collection was probably released to make it easier to get Bubonic's works digitally. The page with the list of manga that the chapters are from is listed on the DLsite page here: https://www.dlsite.com/maniax/work/=/product_id/RJ289641.html The manga on the list that don't have a raw here is: