Back in November 2012, Docomo (finally...) upgraded its Docomo NEXT Serie to Android 4.
To upgrade, you can either follow the detailed version by Docomo (and many other Japanese websites...).
Full of colours, explanations and diagrams so a 2 years old child can do it:...
...and might waste hours
Or, simply download the two following files:
- ZIP: http://spf.fmworld.net/fujitsu/c/update/nttdocomo/f-05d/update1/top/download/ [from the Wifi connection of your F-05D phone OR your computer]
- APK: http://spf.fmworld.net/fujitsu/c/update/nttdocomo/f-05d/update1/sp/top/download/ [from the 3G connection of your F-05D phone]
In both cases, click the blue box to agree. (同意する)
Extract the ZIP in your INTERNAL SD card, NOT in external_sd.
So you should have a ".enc" file at the same level as "external_sd" (and not inside).
Install the APK on your phone, run it, choose the first option (internal memory) and wait, that's it.