Originally Posted by
Wongo
getting those overnight sleepers from Osaka or Tokyo to Hokkaido really seems like mission impossible from my research...
Why is that? According to hyperdia, you get an itinerary where you leave Beppu at 11.20a (via comfortable transfers at Kokura, Himeji and Tokyo, taking shinkansens that are not Nozomi or Mizuho) and arrive Fukushima at 22.16p where you can transfer to a sleeper train that gets into Hakodate the next day at 6.35a.