MySQL 5.6 リファレンスマニュアル (含むMySQL Cluster 7.3-7.4マニュアル)http://dev.mysql.com/doc/refman/5.6/ja/index.html
MySQL Enterprise Monitor 3.0.18 マニュアルhttp://dev.mysql.com/doc/mysql-monitor/3.0/ja/index.html
MySQL Enterprise Backup ユーザーズガイド (バージョン 3.11.1)http://dev.mysql.com/doc/mysql-enterprise-backup/3.11/ja/index.html
If you cannot read this, it's because your Japanese isn't any better than mine. :-)
Jokes aside, as of June 4, 2015, some of the MySQL documentation is available in Japanese now. The biggest book that was translated is the MySQL 5.6 Manual, thousands of pages. The other books, covering MySQL Enterprise Monitor 3.0 and MySQL Enterprise Backup 3.11, are considerably smaller, but all of the translations are complete.