This actually relatively simple on a Mac. All you have to do is go to International settings in Preferences and select check Japanese as an input language. Then

This actually relatively simple on a Mac. All you have to do is go to International settings in Preferences and select check Japanese as an input language. Then you can select between the character sets and languages from the menu bar (or your desired hotkey). One of the major reasons I switched to a Mac was because font rendering was a lot clearer for East Asian languages.