Two free days (Tohoku)

Chubu- and Tohoku-Trip in February

Plan was:
- Tokio - Sendai (1N)
- Yamadera/Yamagata (1N)
- Nyuto Onsen (1N), for a "real" traditional rotenburo experience
- Yokote/Akita (1N), visit Yokote Kamakura Matsuri
- Hachinohe (2N), visit Hachinohe Enburi Matsuri

There is no room available in Tsurunayu Onsen/Nyuto Onsen. - (By the way, does anyone know how long in advance one has to book this popular onsen?)

Any ideas what to do between the visit in Yamadera und the Yokote Kamakura Festival??

How about a night at Zao Onsen? They should have snow monster illumination at that time too. Kakunodate is lovely too. There's lots of accommodation available in Morioka as well.

Have you looked at other accommodation options at Nyuto Onsen?

As PP said you can look into other accommodations at Nyuto onsen or Tazawa Lake area. The onsen are open for day guests as well, so you can still enjoy the traditional rotenburo even if you are not staying in the ryokan.

Otherwise you could visit Kakunodate, which is not very far from Tazawa Lake, so on your route.

Enjoy your trip to Japan!