Please check these keyboard shortcuts for Japanese IME.
ALT-~ (tilde): Cycles between kana and direct input mode
ALT-SHIFT: Cycles through available languages
ALT-CAPS_LOCK: Switches to katakana input mode
CTRL-CAPS_LOCK: Switches to hiragana input mode
SHIFT-ALT: Switches between English mode and Japanese mode.
Control - ~: Switches between the current input mode and the English mode within the Japanese IME.
TIP: Switching between Hiragana input mode and Direct Input mode through the language bar is tedious. Instead you can switch by pressing Alt-Tilde (the key below ESC on your keyboard). So, if you need to type Japanese, press Alt-Tilde and start typing. When you are done press Alt-Tilde again to switch back to English. To achieve the same result when in Japanese mode, press Control - ~.
Hope this answers your question