http://1drv.ms/13luKS4
Stock keyboard lacks Japanese input, so using Swype is the best here (full English + Japanese qwerty keyboard, japanese pen input, and JAPANESE SWIPE INPUT!!).
FYI: For those wanting to make backups prior to messing with the system apps.
1) Use Towelroot to root the phone.
2) Install 3C Toolbox from the Play store (free). (You may also need to install the xposed framework apk as well, plus anything else like BusyBox that the 3C toolbox may ask you to install.)
3C is HIGHLY recommended - you can clear cache, ODEX, backup, system file explorer, monitor system, etc, etc. - slew of free features that put most other system apps to shame.
Also, 3C is a MUST once you decide to tether forever for free using the other post in the Metro F6 thread (WiFi Tether + 3C to kill hostap process).
3) Use this to backup and restore apps (system and user) to your microSD card.