Handwriting Recognition in Mozc (and fixing it)

Mozc is (the open-source subset of) Google’s Japanese IME. It has a kinda-hidden feature of handwriting recognition, which is great for RTK students such as myself which sometimes know how to write a kanji but can’t type it. Usually, Mozc installs to /usr/lib/mozc/, so it can be invoked by:

/usr/lib/mozc/mozc_tool --mode=hand_writing

But sometimes it doesn’t work, and recently I’ve found out more about why.