I tried 8-20 April 2020 departing Sydney, flying to Haneda and then completing a round trip to Osaka (Itami airport) and got $705 return.
You can fly into Haneda, Narita or Osaka Kansai.
It's a good deal if you only want to visit one major location outside of your landing city and save on a JR Pass. For example, Osaka and Sapporo, or Tokyo and Fukuoka.
To book, you need to choose "multiple cities". It's limited to one round trip. There's a list of departure dates on the webpage.
Terms & Conditions: FREE FLIGHTS WITHIN JAPAN
Applicable for customers who purchase Hello Blue Sale promotional fare only.
Applicable Booking Class: Economy Class K
These domestic tickets/sectors must be issued together with International tickets.
Up to one domestic flight can be used per one way when connecting to or from ANA international flight limited to via Haneda, Narita or Kansai airport.
Consumption tax applies for the domestic sectors immediately connecting to/from international flights provided that the connection time between domestic flight and the international flight is more than 24 hours.
Additional airport fees may apply.
I'm a bit confused, what do I put into the search box? do I choose a round trip syd-haneda, then add an additional tokyo-osaka domestic round trip? or is it syd-tokyo-osaka-syd?