3-6 day recs outside of Tokyo/Osaka/Kyoto?

Hello!

I will be in Japan June 4th-July 9th. My current Itinerary is:
June 4-5 — Tokyo
June 6-10 — Kyoto + half day Toei Kyoto Studio Park
June 11 — Nara
June 12-16 — Osaka 2 days, USJ 2 days, and 1 free day (will possibly do a day trip to Kobe or Himeji)
June 17 — Back to Tokyo/rest day
June 18-21 — Tokyo Disneyland and SEA
June 22-29 — Tokyo

I do not have to be back in Tokyo until the 6th of July (hopefully by afternoon but evening is fine). So from June 30 through July 5th I have free time and I am feeling lost over that many days. I thought about spending them in either the Hakone area or Kawaguchiko, but I am starting to second guess those areas and feel like 6 days is too much time at either.

I would love to hear any thoughts on locations where I could reasonably spend 6 days or 2/4 or 3/3 day split areas to visit. But to anything and anywhere so long as I can access it by public transportation since I cannot drive.

July and 6 days, and I d say look into Tohoku. Or even fly up to Hokkaido.

Seconding Tohoku ! There are lots of things to see.
https://www.japan-guide.com/list/e1102.html

I did the following trip in autumn 2022:
Day 1: Tokyo - Hiraizumi
Day 2: morning in Geibikei, afternoon in Morioka, night near Tazawako station
Day 3: morning in Dakigaeri valley, afternoon in Kakunodate, second night near Tazawako
Day 4: Naruko gorge and onsen
Day 5: Sendai
Day 6: morning at Yamadera, night in Zao Onsen
Day 7: Ginzan Onsen
Day 8: back to Tokyo

I particularly liked Hiraizumi, Yamadera and Ginzan onsen. And the big rotenburo in Zao onsen was fantastic, although I'm not sure I would want to have a soak in summer.

If you prefer bigger cities, doing day trips from Sendai is also an option. Morioka is smaller but I think the weather will be better up North.