All of Japan is 110V. Half of that is 50Hz. So for things that time off freq expecting 60Hz (clock on coffee pot) time will be off.
For anything that runs thru transformer, this doesn't matter, so laptop will be okay.
Only problem you may have with plugs is sometimes the one wider prong of a US plug may not fit since Japan's sockets are mostly fitted for plugs with two skinny prongs, not the wider one US uses.
Looking at the plug on my US Vaio laptop transformer, and both prongs same size.