Step One

Choose preferences.

Step Two

Choose Language & Region.

Step Three

Push the + button to add any languages you'd like to use. Then click the "Keyboard Preferences..." button.

Step Four

Under the Input Sources tab select Japanese and scroll through the options and decide how you would like to use the Japanese keyboard.

Step Five

Under the Shortcuts tab choose what keys you'd like to use. You're all set up to type in Japanese on you Mac.