Key Layout of Japanese

Hy

I'm a Linux Newbie and try to get all the things running what I liked to use in Windows. The actual step is the virtual keyboard.
I need to be able to write in Japanese on my Computer, what need some different keys. The Japanese keyboard also have more keys. To use the missing signs i need a virtual keyboard.
I have installed Onboard and all Japanese language packs i found. Also is Anthy finally working. I'm using Linux Mint Sylvia cinnamon.
I didn't found something in the Internet to solve that problem, and I'm not able to program something by my own. So it would be fantastic to have some help here.

Many thanks ;-)