Japanese sleeper trains have been seriously cut back, unfortunately. There's the Sunrise Izumo and the Sunrise Seto which run from Tokyo, but very, very, stupidly, there is no sleeper train from Tokyo to Sapporo. The Cassiopeia was a top tier sleeper train that was cancelled before the Shinkansen even reached Sapporo. I believe they still run a few services each year as cruise trains, but those look to be exorbitantly expensive. Also lacking from the sleeper train roster is the lovely Hokutosei which was a more modest train that still had some very nice features.