Many thanks to Ayako for the link!
Amazon is offering ebook 47 Ronin: The Legend Reborn at no charge for those with kindles or tablets who are interested. The entry says that there is free international wireless delivery via Amazon Whispernet. Ayako has tweeted that she can not see it in Japan so it is not clear if there is some level of geoblocking going on.
The reviews indicate that it is a summary of the legend and movie with photos from the film. Some appreciated it and others saw it as an advertisement for the film. If anyone downloads it, let us know how it is in the comments.