Another sale from Jetstar to Japan.
I just booked a return flight from the Gold Coast to Toyko direct for $360 return in late November - early December. Looks like they are using the roomier 787 planes so should be relatively comfortable for cattle class (compared to Air Asia anyways).
One way fares for reference so you can play around with the return flight to see the cheapest fare:
OOL-NRT 06 Jun 2017 - 26 Jul 2017
OOL-NRT 05 Oct 2017 - 07 Dec 2017
OOL-NRT 15 Jan 2018 - 31 Jan 2018
Example of a ~$360 return flight OOL-NRT:
10:30AM 26 November 2017 - $199
08:25PM 10 December 2017 - $161.68
There may be sales departing from other cities.
Sale ends 11:59PM Monday 10 April 2017.
Cheapest I could find (from GC > Narita) was around $500 (regardless of time period).