freecia

You can store a bag at the airport for up to two weeks and the Tokyo hotel can also takkyubin a bag to the airport (takes a few days notice) to a luggage storage facility. Offload a bag or even two before you fly or take the train up north.
Haneda: https://tokyo-haneda.com/en/service/...checkroom.html
Narita: https://www.narita-airport.jp/en/service/svc_06
Airport TA-Q-BIN | Living in Japan | YAMATO TRANSPORT and List of Pickup / Shipping Counters | Living in Japan | YAMATO TRANSPORT

I'm also a fan of Noboribetsu onsen. It also has several mega-ryokan so while it should be potentially less hectic than Tokyo, you'd probably want to look for a smaller property, a hotel-in-hotel renovated room booking, or in-room onsen to avoid crowding in the onsen after dinner (great onsen water, though. Onsen water quality and variety is the draw, here). Avoid non-renovated mega-ryokan tatami rooms as decades of cigarette smoke will have permeated the entire room. Renovated solely non-smoking rooms should be ok. I have taken the bus from the train station but also check if the ryokan runs a free shuttle from a major train station (some of the large ones do) or grab a taxi from the station. I like the taxi, especially if you're staying further from the town center bus stop the town goes slightly uphill. https://www.japan-guide.com/e/e6753....FROM=5350_6750

If you don't really need an onsen village feel and variety of onsen water:
A few newer resorts near Lake Toya with onsen overlooking the lake. They also have nightly summer fireworks https://goo.gl/maps/i6ahNc23pnRA7GGFA or https://goo.gl/maps/oxyenPuu9ghhcfa96
Slightly odd suggestion since I just suggested a smaller property for Noboribetsu - there's several Hoshino resorts in Aomori including Oirase Keiryuu which offer shuttle busses from major stations https://www.oirase-keiryuu.jp/en/access/ near Oirase Gorge if you like hiking.
The Sanriku coast might also be less crowded and has sea views. The area has a lot of small islands near the coast line https://www.japan-guide.com/e/e5025.html with onsen ryokan.