Kiso Valley and Nikko

Hello,

We are visiting Japan in January. We will be arriving and leaving from Tokyo, but want to spend some time - seven days - seeing some of the Nakasendo Trail and Nikko.

We thought we'd start at Tsumago, hike to Magome, then onto Matsumoto. We're not sure how Nikko fits in, but we thought we'd spend two days there using the Nikko World Heritage Pass. So that would leave us with five days in the Kiso Valley; is there a rail pass to cover this trip? Will we need to train it back to Tokyo from Matsumoto and then out again? There are so many train pass options it's hard to work out what would be best!

Thanks so much for your help.