You could use a TTF or something with japanese characters, but those are pretty large (few MBs at least). I just went ahead and implemented system font usage. I used this as a base:
https://github.com/devkitPro/3ds-examples/blob/master/graphics/printing/system-font/source/main.c
The system font has all primary system languages except (I think) some asian ones like taiwanese/chinese. But it's mostly Japanese that's useful anyways.
My search obviously doesn't support Japanese because I would need to customize the keyboard. For searching japanese, I might just add hiragana keyboard layout mode and use python to normalize jap title's kanji into that. But I'm not even bothering with that now.
Also my fuzzy searching is based on this:
https://github.com/forrestthewoods/lib_fts/blob/master/code/fts_fuzzy_match.h
Works well though may want to adjust score values if you want to favor certain matching patterns.