[jhowell]

Are you making a manga to be read on your Kindle? If so then the Kindle Publishing Guidelines section on Creating Fixed-Layout Books with Image Pop-Ups or Virtual Panels lists the metadata that should be present in the OPF file. For page progression direction it states:

<meta name="primary-writing-mode" content="horizontal-rl"/>

Required for Virtual Panels in manga with right-to-left reading order; optional for other fixed-layout books. Defines page rendering order, reading mode, and reader navigation (including Kindle Text Pop-Up, Kindle Panel View, and Kindle Virtual Panels). Valid values are horizontal-lr, horizontal-rl, vertical-lr, and vertical-rl. The default value is horizontal-lr.

The default behavior is horizontal-lr when the page progression direction is left-to-right or not specified. Use the value horizontal-rl to set the page progression direction to right-to-left.

Use the value vertical-rl to set a page progression direction of right-to-left for Chinese, Japanese, and Korean books.