Continuity
A6 bunko page format
The A6 page size (105 by 148mm) of Japan's bunkobon paperbacks, used by Kanonara as its fixed page.
In Japan, bunkobon are "small-format paperback books, designed to be affordable and space-saving," and most are A6, 105 by 148 millimeters. Named for Iwanami Shoten's 1927 Iwanami Bunko series, the format helped turn books in Japan into affordable mass-market goods and remains the standard trim for pocket fiction, light novels included.
Kanonara takes that trim as its fixed page: every chapter is typeset in advance onto A6 pages, and one pagination engine serves the editor, the chapter viewer and the published reader, so a page number means the same page on every device. A6 was chosen because its width is already close to a phone's, so the fixed page needs almost no shrinking even on the narrowest screens.