Fcitx5 and Mozc turn your plain Latin keyboard into a kana machine — here's the ten-minute setup, including the Wayland gotcha everyone hits.

You do not need a Japanese keyboard to type Japanese. That is the first thing to unlearn. Japanese input on Linux is not about hardware at all — it is about software that watches your romaji keystrokes and converts them, live, into hiragana, katakana, and kanji. Type "konnichiha", hit space, and こんにちは appears. The keyboard never changed. Your understanding of what a keyboard does just did.

On CachyOS, the stack that pulls this off is Fcitx5 plus Mozc. Think of Fcitx5 as the framework — the universal input-method layer that sits between your keystrokes and your applications — and Mozc as the engine that actually knows Japanese. Mozc is Google's open-source Japanese IME (the same lineage as Google Japanese Input), so its conversion predictions are genuinely good. Fcitx5 itself handles the plumbing: which apps get the input, how you toggle languages, where the candidate window appears.

One command to install

Everything you need lives in the Arch/CachyOS repos:

sudo pacman -Syu fcitx5 fcitx5-mozc fcitx5-configtool fcitx5-gtk fcitx5-qt noto-fonts-cjk

That gives you the framework, the Mozc engine, the graphical config tool, toolkit bridges for GTK and Qt apps, and CJK fonts so the characters actually render instead of showing tofu boxes. No AUR packages, no manual builds.

The Wayland gotcha

Here is where most people trip. First, check your session type:

echo "$XDG_SESSION_TYPE"

On KDE Plasma Wayland — the recommended path — do not launch Fcitx5 from autostart scripts or your shell config. KWin wants to start it itself: open System Settings, go to Input & Output → Keyboard → Virtual Keyboard, select Fcitx 5, apply, and log out and back in. If you also launch it manually you will get the classic warning — Fcitx should be launched by KWin under KDE Wayland — and a second, confused instance fighting the first.

On X11, it is the old-school way: autostart Fcitx5 and export the input-method variables (GTK_IM_MODULE, QT_IM_MODULE, XMODIFIERS) so every toolkit knows where to send keystrokes. Xwayland apps on a Wayland session sometimes need those variables too, even when native Wayland apps work fine without them.

Actually typing Japanese

Open the Fcitx5 config tool, add Mozc to your input methods, and set a toggle shortcut (Ctrl+Space is the classic). Then the flow becomes muscle memory: type romaji, watch it become hiragana underlined as a preedit, hit space to pull up kanji candidates, enter to commit. Switching between hiragana, katakana, and direct (Latin) input is a keypress away inside Mozc's own mode switcher.

If nothing happens in a specific app, run through the usual suspects: is Fcitx5 actually running (pgrep fcitx5)? Did the app start before Fcitx5 did (restart the app)? On X11/Xwayland, are the *_IM_MODULE variables set in the environment the app inherited? Nine times out of ten it is one of those three.

Going deeper

This covers the working setup; the edge cases — per-app quirks, diagnostics, clean uninstall — are documented step by step in the companion guide: Install and Use Japanese Keyboard on CachyOS. It walks the full KDE Plasma Wayland and X11 paths, Xwayland application fixes, and a troubleshooting checklist.

Background reading if you want the full picture: the Arch Wiki Fcitx5 page documents every environment variable and toolkit integration, and Mozc upstream explains the engine itself. But honestly? Install the five packages, let KWin start Fcitx5, add Mozc, and you will be typing こんにちは before your coffee cools.