Tohoku will be covered with snow so there are many beautiful places.
One of the most famous winter sights would be Mt. Hakkoda. It's a great ski mountain if you do skiing or snowboarding. Even if you don't, you can climb up all the way to the top with gondola and you can see frost-covered trees.
Also Oirase Gorge in Aomori Prefecture does snow hike tours during winter. I went there before and it was a very magical experience. The quiet forest covered with snow and ice was amazing. You can see the report from here: https://hubjapan.io/articles/oirase-gorge-snow-hike-in-winter-was-the-most-magical-experience
There are many local specialties that will be at its best in winter. Such as Kiritanpo hotpot from Akita. It must feel more delicious to have some hotpot in winter. Apples from Aomori Prefecture will become the best season. :P