1591 Japan ISOT off the coast of France 100 AD

  Interesting idea and he will have a clear technological edge given better metallurgy and some use of gunpowder weapons.  However Japan will have issues of climate, possibly affecting food supply as well and facing a totally foreign culture across whatever water gap separates them from Europe.  Plus the Roman empire is at its height at the moment and has a substantial military and still fairly strong internal culture so a successful conquest could be beyond Hideyoshi although Japanese forces are going to do a lot of damage to the western empire at least.  I can't see him 'conquering Europe' as the continent is too large and alien to him given the technology of the time.