There are individual FLOSS people here, but oftentimes all working in isolation from one other, mostly underground, and it's rather tiny.
Even then, it feels like all the bigger names are all just foreigners who either are bilingual Japanese + something else, or don't speak the language and just rely on their wifes (or husbands) for translation, and occasionally you'll get actually monolingual people too.
Compared to most other countries in the world, even with everyone included the FLOSS scene here is extremely tiny.

And anyone trying to actually compete with the long established proprietary bloat will get stopped in some way.
I bet that if one day XMPP or Session (or something else) would gain too much attention, then Naver (the Korean company behind LINE) will bribe the government to either make propaganda against their FLOSS alternatives, or make it as hard as possible for those to even appear in any media.
Sounds to be very far fetched, but if Nintendo can create a collective of AAA companies to destroy the internet, I mean fight piracy, then this might be a possibility as well, and just frame FLOSS as a piracy.