The survey was conducted in April 2013, about 4 months after the previous survey, and it showed that the newly launched Japanese iBookstore (then only a month old) was now the second most popular ebookstore in Japan. About 16% of survey respondents currently buy ebooks from Apple, with another 13% having done so in the past.
This puts iBooks in a distant second to the Kindle Store, which 49% of the respondents said that they shopped at regularly (another 8.7% had shopped there recently), but it also puts iBooks ahead of Kinokuniya Kinoppy (14.7% currently buy ebooks and 14.6% had shopped there recently), the Sony Reader Store (9.6% and 6.5%, respectively), and Kobo (7.6% and 8.8%).
If you add up these numbers you might notice that they don't quite equal 100%. That's okay because this is a survey of consumer behavior, not market share. If you look at the full chart (here), you'll quickly get the impression that many of the respondents are buying ebooks from more than one ebookstore, hence the overlap.
This survey report is based on responses from readers of OnDeck Weekly, a digital trade magazine which covers the Japanese digital publishing industry. 646 readers responded.