Tokyo to West Japan, no JR rail pass

Flew in to Tokyo and will return home from Haneda as well but there are things in west Japan I would like to see. Thought of buying a regional rail pass as I did not be able to aquire a Japan Rail Pass before my trip this time.

The only regional pass that cover the trip to Osaka is Hokuriku Arch pass, but I would have to get another pass after.

The plans span at least to Onomichi, to see the Shimamami Kaido, and possibly Yamaguchi, to visit Hagi. And to go by ferry from Kobe or Himeji to Shodojima.

Not sure if flying would ease the cost or just be a hassle or if there are any discount tickets for return travel by Shinkansen. I think the air fares are rather high since the JAL/ANA pass discontinued.

I'm not sure if you want to get the Hokuriku Arch Pass if you're not going to explore Kanazawa. I'd probably consider taking a highway bus from Tokyo to Kyoto/Osaka if you think the bullet train is too expensive.
For regional passes, you can get a few for Tokyo and for Kyoto/Osaka/Kobe/Himeji.

Passes for Tokyo:
https://visitjapan-vegetarian.com/the-ultimate-guide-to-tokyos-transpo...

Passes for Osaka/Kyoto/Nara:
https://visitjapan-vegetarian.com/the-most-useful-transportation-passe...

Bus / train / plane to Kansai. You choice. Not pass options.

Then use the appropriate JR West pass to suit your itinerary needs in Chigoku.

Thought of buying a regional rail pass as I did not be able to aquire a Japan Rail Pass before my trip this time.

I think you can still buy it while in Japan, online?
https://japanrailpass.net/en/purchase/online/

For Hagi, there's this regional pass that is a real bargain (too good of a bargain apparently, since they are stopping the sales next month T_T)
https://www.westjr.co.jp/global/en/ticket/pass/sanin_okayama/
But beware, you cannot pick it in Hagi, only in Matsue/Osaka/Okayama/Tottori.