REST is the way the web was designed to work. Thinking of URLs as resources is a guiding principle that aids design of web applications and brings order to URLs.
Browsers traditionally considered URLs to represent pages that would be shown on a single browser window, with the exception of frames. The Kamishibai approach considers URLs to represent fragments of pages. This is similar to frames.
The problem with a one-to-one correspondence between REST URLs and pages is that pages have a lot of redundancy. A single web page shares a lot of common elements with other pages. It is much more efficient to manage web resources at a fragment level.
When we think of URLs as HTML fragment resources, then we can rethink what the root path stands for. In the fragment model, the root path stands for the boot loader, the initialization of the application. It does not stand for any particular page. Therefore, it is actually more natural to use the hash as the navigation indication. The hash based approach is no longer a hack; it is representative of how the web application works.
Another way of seeing it is to rethink what the hash originally stood for. The hash was a way to tell the browser which portion of the web page to show. We can frame the Kamishibai concept in the same way; In Kamishibai, the hash indicates the ID of the HTML element that we want to display in the front. In some cases, the HTML element will already be loaded, which makes it virtually identical to how regular hashes are handled by default. If the HTML element is empty or has not been loaded, Kamishibai loads that page via AJAX. However, this is invisible from the HREF. The HREF simply tells the browser that it wants to view a certain fragment within the root URL resource. It is Kamishibai’s responsibility to prepare that page and display it with animations.
Therefore, we can think of Kamishibai as actually adhering to REST principles. Since it does not alternate the response based on whether it is an AJAX request or not, in some ways it adheres more closely that PJAX.
Looking at the Kamishibai world from a REST perspective, the root URL which holds the whole application can be thought of as a huge single page that you can navigate through with hash links.