G'day Rezz,
Id have to agree with Ant, although you havent made a "backup plan" to come back home with, the life experience that you gained in Japan and the fact that you lived over there teaching English independantly will prove to be an advantage for you when you get back to Perth. Another positive from your time in Japan is you have gained a strong insight about Japanese culture and language, this is a valuable asset for you in your future endeavours.
The fact that you may have lost interest in the country is probably because you have exhausted your options maybe? Having teaching as the only real source of income without other avenues to explore would do the same to anyone.
Good luck
Michael