IIRC the Nexio and the Sig III both have a 5-inch screen at 800x480 resolution.
As for the original question... I think Monster Chinese supports Japanese codes as well. Not sure if it'll work, but try the HPC version - scroll all the way down
http://www.mactiontech.com/download_monster_chinese.htm
(sorry for all the Chinese, but for some reason they link to the same download page from their English site
)
Also I used to use Big Axe Chinese by Gismosoft for the Jornada, but that company seems to have disappeared from the web
I still have the trial installer, which never expires for viewing functions
(only the input part expires
). This I know works for Japanese, because I tried it on the Jornada and viewed some Japanese websites. Even tho I cannot understand it, I could tell the characters were decoded properly
(some characters match the images, hehehe
). If you want I can email it or upload it right here. It's 4.55 MB tho.
However since I don't have a Nexio, I don't know if either one will work for you at all