I have never been able to sleep on an overnight bus in Japan, but I might just have to give this one a try sometime.
It is worth noting that, if you book well in advance, between Tokyo and Osaka, flying is almost always cheaper than the bullet train. The great thing about the bullet train is that you can travel on a whim (I have bought tickets three minutes before boarding a train), but it’s pricey… and booking in advance doesn’t really make it any cheaper.
