I developed this idea on my DS, where the pictochat input system allows you to easily input japanese or english characters. I wanted to do something like leet speak but with japanese characters instead of letters and numbers.
Eventually I settled on a set of japanese characters that look similar enough to english letters that it is readable without too much trouble.

Turns out that FA journals don't support japanese characters, but comments do so I'll put the examples in as comments.
See if you can decypher them.