Earlier quoted context omitted.
A blockchain might actually be a decent solution for this. Just make it so the tokens don't have value.
If all your target users are comfortable with the tradeoffs of systems built on blockchains (ie private key is the source of authority), you're probably looking for Nostr.
Naturally you will find lots of bitcoin people using and developing clients (hence the Lightning integration on most clients) but apparently it has been picking the interest of other groups. There seems to be a thriving Japanese community.