to catch up those who aren't aware, the overwhelming majority of native Japanese speakers use 12-key flick input to type on smartphones, as it evolved from the input on flip phone (garakei) hardware keypads. it also requires less keystrokes => faster than typing romaji, once accustomed.

for context, the most widely recommended Japanese keyboard on android has been Google Gboard, MS Swiftkey, etc. tbh, these are very good as a keyboard, but unfortunately also great at collecting personal private data. the previous open source choice Mozc (created by a Google from a gentler timeline) has been outdated since before the pandemic.

thankfully, now there are at least 3 open source projects working on east Asian language (primarily Japanese) flick keyboards for mobile devices:

FCITX, FUTO keyboard, and Florisboard

so far, i think FUTO seems the furthest along, with a nightly build for android available already. if you try this, remember to import the kanji conversion dictionary file linked in this comment since it was excluded from the apk to reduce file size.

this is very exciting, as only a year ago, there was hardly any mention of work being done. the only solution i could find for modern smartphones was by a Graphene OS forum user who had recompiled the latest binary of Mozc (from 2019!) while splicing in modern components for those that had become outdated. the result was janky to say the least.