Some of the stores, including Kindle Store, held summer vacation campaign to boost the sales, while au Book Pass ranked at the 2nd place thanks to free-reading service for its subscribers.
No.1 Kindle Store: http://www.amazon.co.jp/kindle-tezuka-osamu (1)
No.2 au Book Pass: http://www.bookpass.auone.jp/info/bookpass/pc/ (3)
No.3 eBook Japan: http://www.ebookjapan.jp/ebj/ (2)
No.4 Reader Store: http://ebookstore.sony.jp/ (7)
No.5 iBooks: https://itunes.apple.com/jp/app/ibooks/id364709193?mt=8(5)
No.6 BookLive!: http://booklive.jp/ (4)
No.7 Google Play: https://play.google.com/store/books?hl=ja (6)
No.8 Comic Cmoa: http://www.cmoa.jp (8)
No.9 Honto! E-book store: http://honto.jp/ebook.html (#)
No.10 Kinoppy: http://k-kinoppy.jp/ (-)
The figure in parentheses means the previous rank. “#” means the store was ranked below the 10th last time.
No. 11：Yahoo!Japan Book Store
No. 14：dMarket Book Store
No. 15：LINE Manga
No. 16：Handy Comic
No. 17：Hikari TV Shoten
No. 18：Manga Zenkan.com
No. 19：Nico Nico Seiga
No. 20：Itsudemo Book Store
Refer to this ranking when you are looking for an e-book store.
The next ranking will be released on September 25 (Thursday).