I don’t think this is going to last for very long, given how few date combos at these prices I could find, and some started vanishing as I was tidying up. So if you want it, I suggest jumping on it quickly. Next cheapest is usually Philippine Airlines who come in around the mid 700s, have the same flight path and stopover airport as Cebu Pacific.
Airline: Cebu Pacific
From: Melbourne
To: Tokyo, Japan
Price: From $541. Return.
Bags: carry-on included
