After learning Cangjie, I asked several people if they were aware of any shape based input method for Japanese. Always they replied it didn't exist. I asked a couple of Japanese too; same response. Then to my great surprise, I was trying Boshiamy a couple of days ago and accidentally discovered it could type Japanese!
I haven't been able to locate any Boshiamy tutorials in English so far. So I don't really know how efficient a method it is. Nonetheless, I could type both the Kana and Kanji! What a pity that Cangjie doesn't offer a version for Japanese.