In readiness for the imminent arrival of BA/ amex companion vouchers and th necessity to jump on availability as soon as tickets are released, I am doing some initial planning formations to get to Sydney to visit family. One option I am considering is to fly via Tokyo and spend unto 14 days in Japan, most probably on the way there.

We have been to Japan several times but never in winter. Not interested in skiing but love good food, scenery, culture etc. Not interested in Kyoto as we have been several times (and the last time the hordes of Chinese tour groups put us off returning) . A quick delve into AI came up with Tokyo , Kawaguchiko (Fuji) , Matsumoto, Takayama/Shirakawa-go, Kanazawa . We would travel by train where possible, most likely utilising a JR Pass. Another option might be the snow & ice festival in Sapporo?

For reference, on previous trip we have visited Tokyo, Kyoto, Nara, Koyasan, Takayama Himeji. One city we haven't been to is Osaka and I am wondering whether it is viable to skip Tokyo and go straight there.

Any thoughts or suggestions would be much appreciated

You might look into Okinawa. A quick flight from Tokyo or Osaka, with comfortable temperatures. The Chinese New Year is mid-February, so sounds like you may avoid the Chinese tourists flocking to Okinawa.

Shirakawago is a wonder under multiple feet of snow. The Koemon gassho zukuri where I stayed had snow boots for guests.
The Sapporo Snow Festival should be fun.
It will be the beginning of plum blossom season while you are there. You might find a festival somewhere south of Tokyo, more likely toward the end of your visit.

Do your dates work for the Yokote Kamakura Festival?
https://www.japan-guide.com/e/e3690.html

Other than that, I'd suggest Shikoku and Kyushu.
Both are OK in winter.

I went there in February 2020....very interesting!!

Thanks for the input. Very useful and I shall bear it in mind and will no doubt return with further questions when we have finally decided which route to take to Australia.

Thanks for the info on the Yokote Kamakura Festival - looks amazing, I need to check the dates of the Aussie school holidays , but that looks as if that could work if we go on the way back to London. I suppose we could split our time in Japan into two session on the way out and back. The main reason for wanting to hit Japan on teh way out was to try and avoid dealing with jet lag and grandkids at the same time!

FWIW, ANA has nonstop flights between Sapporo (CTS) and Akita (AXT) for $54. That would make it easy to go to both the Snow Festival and Yokote Kamakura Festival.

Both airports have flights to Tokyo HND, of course, and to Osaka ITM. There are several domestic nonstops from Sapporo (Fukuoka and Hiroshima, ime, and Okayama) so it would be easy to get to Kyushu (Fukuoka) or Shikoku (rail from Okayama or boat from Hiroshima).

Thanks. Good to know. I was thinking of the JR pass to get around as I try to avoid flying for short domestic flights wherever possible. However, I understand that the cost of the passes has risen significantly.

Tokyo to Akita is about 18,000 yen and just under 4 hours on the shinkansen
Akita to Sapporo would be maybe 18,000 and a long trip maybe 8 or 9 hours. Transfers at Shin-Aomori and Shin-Hakodate and 7.5 hours actually on the three trains.
Sapporo to Tokyo is about 33,000 yen and almost 9 hours on a limited express to Shin-Hakodate and then shinkansen to Tokyo.

JAL has 3-cabin widebody A350 on Tokyo-Sapporo-Fukuoka-Tokyo (I flew those in 2023). Tokyo Haneda to Sapporo would be $130 in a comfy business class and take 1.5 hours. Half that in economy. Or from Narita it could be $35+ in economy on Jetstar to Sapporo.

A JR Pass or regional pass could work for you. Tokyo and Akita are in JR East region.

You can use the calculator (be sure to set preference to exclude flights): Japan Rail Pass Calculator - find out whether a JR Pass pays off

It doesn't have Akita as an option but could use Aomori which is 3 hours from Akita 5000 yen

Japan also has "highway" buses including overnight/long-haul and some are fancy with sleepers.