Multi-Day Hike for Anniversary

Salutations!

We’re coming to Japan in late April for a convention. This will be my 3rd trip, my partner’s 2nd trip. As it happens, our anniversary is the weekend after.

I considered finally taking him to Kyoto and Osaka, but those feels so overrun right now that we’re thinking of saving them for a future visit when the Japan frenzy has calmed some. thanks for the "encouragement" to do it anyway, but we're actually quite excited about the idea of hiking anyway now; not sure why I'm getting downvoted for this sentiment

We like hiking and backpacking (we live in the Sierra Nevada Mountains and I spent 5 months hiking the Pacific Crest Trail last year), so I’m thinking of trying a trail in Japan.

As this would be our first hiking excursion (beyond short day ones) in Japan, I don’t want to bring all the backpacking gear. Also, it is our ten year anniversary, so I would love to do something where we’ve got the chance to stay in some celebration worthy accommodations along the way.

We’ve got roughly 5-6 days and can easily clear 15-20 km/ day on typical US trails (obviously slower going for cobble stone paths).

We’re fine with “lower scale” accommodations, too, if that’s all that available, but would be nice to at least end on “higher scale” ones in a cool town for a day or two.

I’d prefer to “complete” a trail, but this isn’t firm and I’m open to doing just a section if it fits other criteria.

I’ve looked into a few options that seem interesting, but it really just has me wondering what this community’s ideas are. No budget restrictions or distance from airport restrictions - I’m hoping to save this for future ideas and trips!