Below is my Japanese-English dictionary based on EDict2. It has been created as a replacement of original Kobo Japanese dictionary.
To install just copy (and replace) dicthtml-ja.zip file in .kobo/dict folder in your Kobo reader.
It would be a good idea to do a backup of the dicthtml-ja.zip file before overwriting.
Warning: The file cannot be used as Japanase-English translation dictionary. It means you cannot change the name of the file and add it as an additional Kobo dictionary - it will not work this way!