I am actually trying to plan something similar, but for a family of 4 with 2 kids age 10 & 5. My wife and I visited Hakone on a prior trip and would like to visit another onsen town. I prefer a place that has more character but with somewhat modern amenities. (I don't really like an onsen city/town with a bunch of tall concrete buildings.) A ryokan with an outdoor onsen that allows reservation for private use or in-suite onsen a big plus. We will also be utilitzing JR pass. Any recommendation? If nothing fits those description between Tokyo and Kyoto, what about between Kyoto and Hiroshima?