I recommend fcitx-mozc for Japanese Input Method in Arch or Angergos, and I'm also using it. I think fcitx-mozc is better than ibus-mozc for some reasons. First one is that there are official binary package of fcitx-mozc, but ibus-mozc is only in AUR. Secondly, fcitx is more configurable than ibus.
Please see https://wiki.archlinux.org/index.php/Fcitx for way of installing and configuring fcitx.
After that, you can configure alternative keybind of "Zenkaku-Hankaku."
Since I'm using US keyboard, I set C-\
(Control + \
) for Zenkaku-Hankaku
key. The option is at
"Configure" (at fcitx's menu, appears after right-clicking fcitx icon or run `fcitx-configtool` on terminal) > "Global Config" > "Trigger Input Method."
You can switch on or off to use input method with key on that config, or switch between all of installed input methods.